feat(tools): rnote-style toolbar core writing batch

Replace the ad-hoc tool palette with a shared tool system
(EditorToolKind) across the PDF, note and slide editors, and add
the core writing tools.

- Multiple brushes, each remembering its OWN color (rnote-style):
  selecting a brush restores its color, changing color updates only
  that brush, and each brush button shows its current color.
- Select tool: tap-select a committed stroke, drag to move it,
  delete it — persisted and undoable.
- Shape tool: line / rectangle / ellipse / arrow, drawn with a live
  preview and committed as generated PenStrokes (shape_geometry.dart)
  so they reuse stroke rendering, erase, persistence and undo.
- Highlighter + eraser fold into the same tool system.

Text/bookmark/search+OCR/backgrounds/Windows-Ink are later batches
(TODO). Brush opacity still deferred. analyze clean, 302 tests.

lib/editor/canvas/pen_palette_widgets.dart

@@ -8,6 +8,7 @@ import 'package:flutter/material.dart';
 
 import '../../l10n/app_localizations.dart';
 import '../engine/brush.dart';
+import 'editor_tool.dart';
 
 /// Localized display name for a brush (single source so all three editors agree).
 String brushLabel(BrushKind kind, AppLocalizations l) => switch (kind) {
@@ -28,6 +29,24 @@ String brushLabelEn(BrushKind kind) => switch (kind) {
       BrushKind.highlighter => 'Highlighter',
     };
 
+/// Localized display name for a shape kind.
+String shapeLabel(ShapeKind kind, AppLocalizations l) => switch (kind) {
+      ShapeKind.line => l.shapeLine,
+      ShapeKind.rectangle => l.shapeRectangle,
+      ShapeKind.ellipse => l.shapeEllipse,
+      ShapeKind.arrow => l.shapeArrow,
+    };
+
+/// English fallback shape name (for the note/slide editors which use hardcoded
+/// English strings — see [brushLabelEn]).
+/// TODO(brush-l10n-noteslide): localize the note/slide toolbars wholesale.
+String shapeLabelEn(ShapeKind kind) => switch (kind) {
+      ShapeKind.line => 'Line',
+      ShapeKind.rectangle => 'Rectangle',
+      ShapeKind.ellipse => 'Ellipse',
+      ShapeKind.arrow => 'Arrow',
+    };
+
 /// The brushes selectable as the PEN tool. The highlighter is its own tool, so
 /// it is NOT offered here (eraser is also a separate tool).
 const List<BrushKind> kPenToolBrushes = [
@@ -44,11 +63,23 @@ IconData brushIcon(BrushKind kind) => switch (kind) {
       BrushKind.highlighter => Icons.brush_outlined, // marker
     };
 
+/// Material icon for a [ShapeKind] (used in the shape picker + tool button).
+IconData shapeIcon(ShapeKind kind) => switch (kind) {
+      ShapeKind.line => Icons.show_chart, // straight line
+      ShapeKind.rectangle => Icons.crop_square,
+      ShapeKind.ellipse => Icons.circle_outlined,
+      ShapeKind.arrow => Icons.arrow_outward,
+    };
+
 /// A dropdown that selects the active PEN brush (fountain / ballpoint / pencil).
 ///
 /// Highlighter and eraser remain separate tools. Tapping the button opens a
 /// menu of [kPenToolBrushes]; the chosen brush is reported via [onSelected].
 /// [labelFor] localizes each brush name so the menu honors the app locale.
+/// [colorFor] returns each brush's REMEMBERED color (rnote-style per-brush color
+/// memory): the active brush's color is shown as an underline on the button and
+/// as a dot beside each menu item, so the toolbar makes each brush's color
+/// visible at a glance.
 class BrushPickerButton extends StatelessWidget {
   const BrushPickerButton({
     super.key,
@@ -56,6 +87,7 @@ class BrushPickerButton extends StatelessWidget {
     required this.active,
     required this.onSelected,
     required this.labelFor,
+    required this.colorFor,
     required this.tooltip,
   });
 
@@ -70,6 +102,9 @@ class BrushPickerButton extends StatelessWidget {
   /// Localized display name for a brush.
   final String Function(BrushKind) labelFor;
 
+  /// The remembered color for a brush (drives the underline + menu dots).
+  final Color Function(BrushKind) colorFor;
+
   final String tooltip;
 
   @override
@@ -91,6 +126,17 @@ class BrushPickerButton extends StatelessWidget {
                 Icon(brushIcon(b), size: 20),
                 const SizedBox(width: 10),
                 Text(labelFor(b)),
+                const SizedBox(width: 8),
+                // The brush's remembered color (rnote per-brush color memory).
+                Container(
+                  width: 12,
+                  height: 12,
+                  decoration: BoxDecoration(
+                    color: colorFor(b),
+                    shape: BoxShape.circle,
+                    border: Border.all(color: cs.outlineVariant),
+                  ),
+                ),
                 if (b == selected) ...[
                   const SizedBox(width: 8),
                   Icon(Icons.check, size: 18, color: cs.primary),
@@ -107,11 +153,26 @@ class BrushPickerButton extends StatelessWidget {
           color: active ? cs.secondaryContainer : Colors.transparent,
           borderRadius: BorderRadius.circular(20),
         ),
-        child: Row(
+        child: Column(
           mainAxisSize: MainAxisSize.min,
           children: [
-            Icon(brushIcon(selected), size: 22, color: iconColor),
-            Icon(Icons.arrow_drop_down, size: 18, color: iconColor),
+            Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Icon(brushIcon(selected), size: 22, color: iconColor),
+                Icon(Icons.arrow_drop_down, size: 18, color: iconColor),
+              ],
+            ),
+            // Per-brush color underline: shows the active brush's remembered
+            // color so switching brushes visibly switches the color.
+            Container(
+              height: 3,
+              width: 24,
+              decoration: BoxDecoration(
+                color: colorFor(selected),
+                borderRadius: BorderRadius.circular(2),
+              ),
+            ),
           ],
         ),
       ),
@@ -119,6 +180,87 @@ class BrushPickerButton extends StatelessWidget {
   }
 }
 
+/// A toggle-style tool button that doubles as a [ShapeKind] picker: a short tap
+/// activates the shape tool with the current shape; a long-press (or the dropdown
+/// caret) opens the line / rectangle / ellipse / arrow submenu.
+class ShapePickerButton extends StatelessWidget {
+  const ShapePickerButton({
+    super.key,
+    required this.selected,
+    required this.active,
+    required this.onActivate,
+    required this.onSelected,
+    required this.labelFor,
+    required this.tooltip,
+  });
+
+  /// The currently selected shape kind.
+  final ShapeKind selected;
+
+  /// True when the shape tool is the active tool — drives highlight.
+  final bool active;
+
+  /// Called when the button body is tapped (activate the shape tool).
+  final VoidCallback onActivate;
+
+  /// Called when a shape kind is picked from the submenu (also activates).
+  final ValueChanged<ShapeKind> onSelected;
+
+  /// Localized display name for a shape kind.
+  final String Function(ShapeKind) labelFor;
+
+  final String tooltip;
+
+  @override
+  Widget build(BuildContext context) {
+    final cs = Theme.of(context).colorScheme;
+    final iconColor = active ? cs.onSecondaryContainer : cs.onSurfaceVariant;
+    return PopupMenuButton<ShapeKind>(
+      tooltip: tooltip,
+      initialValue: selected,
+      onSelected: onSelected,
+      itemBuilder: (context) => [
+        for (final s in ShapeKind.values)
+          PopupMenuItem<ShapeKind>(
+            value: s,
+            child: Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Icon(shapeIcon(s), size: 20),
+                const SizedBox(width: 10),
+                Text(labelFor(s)),
+                if (s == selected) ...[
+                  const SizedBox(width: 8),
+                  Icon(Icons.check, size: 18, color: cs.primary),
+                ],
+              ],
+            ),
+          ),
+      ],
+      child: InkWell(
+        borderRadius: BorderRadius.circular(20),
+        onTap: onActivate,
+        child: AnimatedContainer(
+          duration: const Duration(milliseconds: 150),
+          margin: const EdgeInsets.symmetric(horizontal: 2),
+          padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 8),
+          decoration: BoxDecoration(
+            color: active ? cs.secondaryContainer : Colors.transparent,
+            borderRadius: BorderRadius.circular(20),
+          ),
+          child: Row(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              Icon(shapeIcon(selected), size: 22, color: iconColor),
+              Icon(Icons.arrow_drop_down, size: 18, color: iconColor),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
+
 /// A Material 3 toggle-style icon button for the floating tool palette.
 class ToolButton extends StatelessWidget {
   const ToolButton({