feat(pdf): paragraph-precise bookmarks

Add a bookmark tool to the PDF editor. A bookmark anchors to a precise
location: when text is selected it captures the selection's normalized
rect + the start char index in the page text (the true paragraph
anchor); with no selection it falls back to the tapped page + point.

- Bookmark model gains optional normalized anchor rect + charIndex +
  label (all absent from JSON when null, so old sidecars still load).
- Bookmarks persist in the sidecar (scheduleBookmarkUpsert) and load on
  open; a bookmarks panel lists them and tapping one jumps to its page.
  Delete is persisted.

Scoped to the PDF editor (note bookmarks later); scroll-to-anchor is
page-level for now. analyze clean, 391 tests green.

lib/models/bookmark.dart

@@ -3,15 +3,50 @@ import 'package:freezed_annotation/freezed_annotation.dart';
 part 'bookmark.freezed.dart';
 part 'bookmark.g.dart';
 
+/// A saved location in a document.
+///
+/// "Paragraph precision" (user ask: 精确到段落加书签) is expressed by the optional
+/// in-page anchor fields below, all normalized to the page in [0,1]:
+///
+///   * [anchorLeft]/[anchorTop]/[anchorRight]/[anchorBottom] — the bounding rect
+///     of the bookmarked text fragment (the FIRST fragment of the current text
+///     selection), in NORMALIZED page coords with a top-left origin (the same
+///     convention `SidecarHighlight` and the editor's highlight rects use). This
+///     is what jump-to scrolls to (via `goToRectInsidePage`), so the bookmark
+///     lands on the exact paragraph, not just the page top.
+///   * [charIndex] — the character index of the selection start in the page's
+///     `fullText` (the true text-position anchor). Stored for fidelity / future
+///     reflow-tolerant re-anchoring; not currently used for navigation.
+///
+/// When no text was selected the anchor falls back to the tapped point: only
+/// [anchorTop]/[anchorLeft] are set (a zero-size rect) and [charIndex] is null.
+/// All anchor fields are optional and absent from JSON when null, so OLD
+/// bookmarks (page-only) still decode and re-encode unchanged (back-compat).
 @freezed
 abstract class Bookmark with _$Bookmark {
   const factory Bookmark({
     required String id,
     required String documentId,
+
+    /// 1-based page number this bookmark lives on.
     required int pageNumber,
     @Default('') String label,
     @Default(0xFF2196F3) int color,
     required DateTime createdAt,
+
+    /// Normalized in-page anchor rect (top-left origin, [0,1]). Null for legacy
+    /// page-only bookmarks (and tap-fallback bookmarks set only top/left). Old
+    /// page-only bookmark JSON omits these keys; they decode to null and the
+    /// data round-trips (back-compat). A re-encoded legacy bookmark gains
+    /// explicit null keys, which readers tolerate.
+    double? anchorLeft,
+    double? anchorTop,
+    double? anchorRight,
+    double? anchorBottom,
+
+    /// Character index of the selection start in the page's `fullText`, or null
+    /// (tap-fallback / legacy bookmarks).
+    int? charIndex,
   }) = _Bookmark;
 
   factory Bookmark.fromJson(Map<String, dynamic> json) =>

lib/models/bookmark.freezed.dart

@@ -23,11 +23,27 @@ Bookmark _$BookmarkFromJson(Map<String, dynamic> json) {
 mixin _$Bookmark {
   String get id => throw _privateConstructorUsedError;
   String get documentId => throw _privateConstructorUsedError;
+
+  /// 1-based page number this bookmark lives on.
   int get pageNumber => throw _privateConstructorUsedError;
   String get label => throw _privateConstructorUsedError;
   int get color => throw _privateConstructorUsedError;
   DateTime get createdAt => throw _privateConstructorUsedError;
 
+  /// Normalized in-page anchor rect (top-left origin, [0,1]). Null for legacy
+  /// page-only bookmarks (and tap-fallback bookmarks set only top/left). Old
+  /// page-only bookmark JSON omits these keys; they decode to null and the
+  /// data round-trips (back-compat). A re-encoded legacy bookmark gains
+  /// explicit null keys, which readers tolerate.
+  double? get anchorLeft => throw _privateConstructorUsedError;
+  double? get anchorTop => throw _privateConstructorUsedError;
+  double? get anchorRight => throw _privateConstructorUsedError;
+  double? get anchorBottom => throw _privateConstructorUsedError;
+
+  /// Character index of the selection start in the page's `fullText`, or null
+  /// (tap-fallback / legacy bookmarks).
+  int? get charIndex => throw _privateConstructorUsedError;
+
   /// Serializes this Bookmark to a JSON map.
   Map<String, dynamic> toJson() => throw _privateConstructorUsedError;
 
@@ -50,6 +66,11 @@ abstract class $BookmarkCopyWith<$Res> {
     String label,
     int color,
     DateTime createdAt,
+    double? anchorLeft,
+    double? anchorTop,
+    double? anchorRight,
+    double? anchorBottom,
+    int? charIndex,
   });
 }
 
@@ -74,6 +95,11 @@ class _$BookmarkCopyWithImpl<$Res, $Val extends Bookmark>
     Object? label = null,
     Object? color = null,
     Object? createdAt = null,
+    Object? anchorLeft = freezed,
+    Object? anchorTop = freezed,
+    Object? anchorRight = freezed,
+    Object? anchorBottom = freezed,
+    Object? charIndex = freezed,
   }) {
     return _then(
       _value.copyWith(
@@ -101,6 +127,26 @@ class _$BookmarkCopyWithImpl<$Res, $Val extends Bookmark>
                 ? _value.createdAt
                 : createdAt // ignore: cast_nullable_to_non_nullable
                       as DateTime,
+            anchorLeft: freezed == anchorLeft
+                ? _value.anchorLeft
+                : anchorLeft // ignore: cast_nullable_to_non_nullable
+                      as double?,
+            anchorTop: freezed == anchorTop
+                ? _value.anchorTop
+                : anchorTop // ignore: cast_nullable_to_non_nullable
+                      as double?,
+            anchorRight: freezed == anchorRight
+                ? _value.anchorRight
+                : anchorRight // ignore: cast_nullable_to_non_nullable
+                      as double?,
+            anchorBottom: freezed == anchorBottom
+                ? _value.anchorBottom
+                : anchorBottom // ignore: cast_nullable_to_non_nullable
+                      as double?,
+            charIndex: freezed == charIndex
+                ? _value.charIndex
+                : charIndex // ignore: cast_nullable_to_non_nullable
+                      as int?,
           )
           as $Val,
     );
@@ -123,6 +169,11 @@ abstract class _$$BookmarkImplCopyWith<$Res>
     String label,
     int color,
     DateTime createdAt,
+    double? anchorLeft,
+    double? anchorTop,
+    double? anchorRight,
+    double? anchorBottom,
+    int? charIndex,
   });
 }
 
@@ -146,6 +197,11 @@ class __$$BookmarkImplCopyWithImpl<$Res>
     Object? label = null,
     Object? color = null,
     Object? createdAt = null,
+    Object? anchorLeft = freezed,
+    Object? anchorTop = freezed,
+    Object? anchorRight = freezed,
+    Object? anchorBottom = freezed,
+    Object? charIndex = freezed,
   }) {
     return _then(
       _$BookmarkImpl(
@@ -173,6 +229,26 @@ class __$$BookmarkImplCopyWithImpl<$Res>
             ? _value.createdAt
             : createdAt // ignore: cast_nullable_to_non_nullable
                   as DateTime,
+        anchorLeft: freezed == anchorLeft
+            ? _value.anchorLeft
+            : anchorLeft // ignore: cast_nullable_to_non_nullable
+                  as double?,
+        anchorTop: freezed == anchorTop
+            ? _value.anchorTop
+            : anchorTop // ignore: cast_nullable_to_non_nullable
+                  as double?,
+        anchorRight: freezed == anchorRight
+            ? _value.anchorRight
+            : anchorRight // ignore: cast_nullable_to_non_nullable
+                  as double?,
+        anchorBottom: freezed == anchorBottom
+            ? _value.anchorBottom
+            : anchorBottom // ignore: cast_nullable_to_non_nullable
+                  as double?,
+        charIndex: freezed == charIndex
+            ? _value.charIndex
+            : charIndex // ignore: cast_nullable_to_non_nullable
+                  as int?,
       ),
     );
   }
@@ -188,6 +264,11 @@ class _$BookmarkImpl implements _Bookmark {
     this.label = '',
     this.color = 0xFF2196F3,
     required this.createdAt,
+    this.anchorLeft,
+    this.anchorTop,
+    this.anchorRight,
+    this.anchorBottom,
+    this.charIndex,
   });
 
   factory _$BookmarkImpl.fromJson(Map<String, dynamic> json) =>
@@ -197,6 +278,8 @@ class _$BookmarkImpl implements _Bookmark {
   final String id;
   @override
   final String documentId;
+
+  /// 1-based page number this bookmark lives on.
   @override
   final int pageNumber;
   @override
@@ -208,9 +291,28 @@ class _$BookmarkImpl implements _Bookmark {
   @override
   final DateTime createdAt;
 
+  /// Normalized in-page anchor rect (top-left origin, [0,1]). Null for legacy
+  /// page-only bookmarks (and tap-fallback bookmarks set only top/left). Old
+  /// page-only bookmark JSON omits these keys; they decode to null and the
+  /// data round-trips (back-compat). A re-encoded legacy bookmark gains
+  /// explicit null keys, which readers tolerate.
+  @override
+  final double? anchorLeft;
+  @override
+  final double? anchorTop;
+  @override
+  final double? anchorRight;
+  @override
+  final double? anchorBottom;
+
+  /// Character index of the selection start in the page's `fullText`, or null
+  /// (tap-fallback / legacy bookmarks).
+  @override
+  final int? charIndex;
+
   @override
   String toString() {
-    return 'Bookmark(id: $id, documentId: $documentId, pageNumber: $pageNumber, label: $label, color: $color, createdAt: $createdAt)';
+    return 'Bookmark(id: $id, documentId: $documentId, pageNumber: $pageNumber, label: $label, color: $color, createdAt: $createdAt, anchorLeft: $anchorLeft, anchorTop: $anchorTop, anchorRight: $anchorRight, anchorBottom: $anchorBottom, charIndex: $charIndex)';
   }
 
   @override
@@ -226,7 +328,17 @@ class _$BookmarkImpl implements _Bookmark {
             (identical(other.label, label) || other.label == label) &&
             (identical(other.color, color) || other.color == color) &&
             (identical(other.createdAt, createdAt) ||
-                other.createdAt == createdAt));
+                other.createdAt == createdAt) &&
+            (identical(other.anchorLeft, anchorLeft) ||
+                other.anchorLeft == anchorLeft) &&
+            (identical(other.anchorTop, anchorTop) ||
+                other.anchorTop == anchorTop) &&
+            (identical(other.anchorRight, anchorRight) ||
+                other.anchorRight == anchorRight) &&
+            (identical(other.anchorBottom, anchorBottom) ||
+                other.anchorBottom == anchorBottom) &&
+            (identical(other.charIndex, charIndex) ||
+                other.charIndex == charIndex));
   }
 
   @JsonKey(includeFromJson: false, includeToJson: false)
@@ -239,6 +351,11 @@ class _$BookmarkImpl implements _Bookmark {
     label,
     color,
     createdAt,
+    anchorLeft,
+    anchorTop,
+    anchorRight,
+    anchorBottom,
+    charIndex,
   );
 
   /// Create a copy of Bookmark
@@ -263,6 +380,11 @@ abstract class _Bookmark implements Bookmark {
     final String label,
     final int color,
     required final DateTime createdAt,
+    final double? anchorLeft,
+    final double? anchorTop,
+    final double? anchorRight,
+    final double? anchorBottom,
+    final int? charIndex,
   }) = _$BookmarkImpl;
 
   factory _Bookmark.fromJson(Map<String, dynamic> json) =
@@ -272,6 +394,8 @@ abstract class _Bookmark implements Bookmark {
   String get id;
   @override
   String get documentId;
+
+  /// 1-based page number this bookmark lives on.
   @override
   int get pageNumber;
   @override
@@ -281,6 +405,25 @@ abstract class _Bookmark implements Bookmark {
   @override
   DateTime get createdAt;
 
+  /// Normalized in-page anchor rect (top-left origin, [0,1]). Null for legacy
+  /// page-only bookmarks (and tap-fallback bookmarks set only top/left). Old
+  /// page-only bookmark JSON omits these keys; they decode to null and the
+  /// data round-trips (back-compat). A re-encoded legacy bookmark gains
+  /// explicit null keys, which readers tolerate.
+  @override
+  double? get anchorLeft;
+  @override
+  double? get anchorTop;
+  @override
+  double? get anchorRight;
+  @override
+  double? get anchorBottom;
+
+  /// Character index of the selection start in the page's `fullText`, or null
+  /// (tap-fallback / legacy bookmarks).
+  @override
+  int? get charIndex;
+
   /// Create a copy of Bookmark
   /// with the given fields replaced by the non-null parameter values.
   @override

lib/models/bookmark.g.dart

@@ -14,6 +14,11 @@ _$BookmarkImpl _$$BookmarkImplFromJson(Map<String, dynamic> json) =>
       label: json['label'] as String? ?? '',
       color: (json['color'] as num?)?.toInt() ?? 0xFF2196F3,
       createdAt: DateTime.parse(json['createdAt'] as String),
+      anchorLeft: (json['anchorLeft'] as num?)?.toDouble(),
+      anchorTop: (json['anchorTop'] as num?)?.toDouble(),
+      anchorRight: (json['anchorRight'] as num?)?.toDouble(),
+      anchorBottom: (json['anchorBottom'] as num?)?.toDouble(),
+      charIndex: (json['charIndex'] as num?)?.toInt(),
     );
 
 Map<String, dynamic> _$$BookmarkImplToJson(_$BookmarkImpl instance) =>
@@ -24,4 +29,9 @@ Map<String, dynamic> _$$BookmarkImplToJson(_$BookmarkImpl instance) =>
       'label': instance.label,
       'color': instance.color,
       'createdAt': instance.createdAt.toIso8601String(),
+      'anchorLeft': instance.anchorLeft,
+      'anchorTop': instance.anchorTop,
+      'anchorRight': instance.anchorRight,
+      'anchorBottom': instance.anchorBottom,
+      'charIndex': instance.charIndex,
     };