feat: OneNote-style notebooks, text fonts, and page navigation

Add notebook.json containers with multi-member pages, fix PDF text
editing (size/bold/drag/double-tap), index SidecarText in search, and
share keyboard page shortcuts plus a PDF scrubber.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/storage/notebook_manifest.dart

@@ -0,0 +1,160 @@
+// lib/storage/notebook_manifest.dart
+//
+// OneNote-style notebook container: a vault folder with `notebook.json` that
+// lists members (blank notes + imported PDF/PPTX/DOCX). Each member still uses
+// its own sidecar; this file is only the table of contents.
+
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+/// Filename of the notebook container manifest inside a vault folder.
+const String kNotebookManifestName = 'notebook.json';
+
+/// Default annotation font family (matches app UI theme).
+const String kAnnotationFontFamily = 'IBM Plex Sans';
+
+/// Kind of a notebook member.
+enum NotebookMemberKind {
+  note,
+  pdf,
+  pptx,
+  ppt,
+  docx,
+}
+
+NotebookMemberKind? notebookMemberKindFromExt(String ext) {
+  switch (ext.toLowerCase()) {
+    case 'pdf':
+      return NotebookMemberKind.pdf;
+    case 'pptx':
+      return NotebookMemberKind.pptx;
+    case 'ppt':
+      return NotebookMemberKind.ppt;
+    case 'docx':
+      return NotebookMemberKind.docx;
+    case 'note':
+    case 'notebook':
+      return NotebookMemberKind.note;
+    default:
+      return null;
+  }
+}
+
+String notebookMemberKindToExt(NotebookMemberKind kind) => switch (kind) {
+      NotebookMemberKind.note => 'note',
+      NotebookMemberKind.pdf => 'pdf',
+      NotebookMemberKind.pptx => 'pptx',
+      NotebookMemberKind.ppt => 'ppt',
+      NotebookMemberKind.docx => 'docx',
+    };
+
+/// One page/section inside a notebook container.
+class NotebookMember {
+  const NotebookMember({
+    required this.id,
+    required this.kind,
+    required this.relativePath,
+    required this.title,
+  });
+
+  final String id;
+  final NotebookMemberKind kind;
+
+  /// Path relative to the notebook folder (POSIX separators preferred).
+  final String relativePath;
+
+  final String title;
+
+  Map<String, dynamic> toJson() => {
+        'id': id,
+        'kind': kind.name,
+        'path': relativePath,
+        'title': title,
+      };
+
+  factory NotebookMember.fromJson(Map<String, dynamic> json) {
+    final kindName = (json['kind'] as String?) ?? 'note';
+    final kind = NotebookMemberKind.values.firstWhere(
+      (k) => k.name == kindName,
+      orElse: () => NotebookMemberKind.note,
+    );
+    return NotebookMember(
+      id: (json['id'] as String?) ?? '',
+      kind: kind,
+      relativePath: (json['path'] as String?) ?? '',
+      title: (json['title'] as String?) ?? '',
+    );
+  }
+
+  NotebookMember copyWith({String? title, String? relativePath}) =>
+      NotebookMember(
+        id: id,
+        kind: kind,
+        relativePath: relativePath ?? this.relativePath,
+        title: title ?? this.title,
+      );
+}
+
+/// Table of contents for a multi-document notebook folder.
+class NotebookManifest {
+  const NotebookManifest({
+    required this.title,
+    required this.members,
+    this.version = 1,
+  });
+
+  final int version;
+  final String title;
+  final List<NotebookMember> members;
+
+  Map<String, dynamic> toJson() => {
+        'version': version,
+        'title': title,
+        'members': members.map((m) => m.toJson()).toList(),
+      };
+
+  factory NotebookManifest.fromJson(Map<String, dynamic> json) {
+    final raw = (json['members'] as List<dynamic>?) ?? const [];
+    return NotebookManifest(
+      version: (json['version'] as num?)?.toInt() ?? 1,
+      title: (json['title'] as String?) ?? '',
+      members: [
+        for (final e in raw)
+          NotebookMember.fromJson(e as Map<String, dynamic>),
+      ],
+    );
+  }
+
+  NotebookManifest copyWith({
+    String? title,
+    List<NotebookMember>? members,
+  }) =>
+      NotebookManifest(
+        version: version,
+        title: title ?? this.title,
+        members: members ?? this.members,
+      );
+
+  static File fileIn(String folderPath) =>
+      File(p.join(folderPath, kNotebookManifestName));
+
+  static Future<NotebookManifest?> read(String folderPath) async {
+    final file = fileIn(folderPath);
+    if (!await file.exists()) return null;
+    try {
+      final map = jsonDecode(await file.readAsString()) as Map<String, dynamic>;
+      return NotebookManifest.fromJson(map);
+    } catch (_) {
+      return null;
+    }
+  }
+
+  static Future<void> write(String folderPath, NotebookManifest manifest) async {
+    final file = fileIn(folderPath);
+    await file.writeAsString(
+      const JsonEncoder.withIndent('  ').convert(manifest.toJson()),
+    );
+  }
+}