fix: PDF finger ink, chrome UX, OneNote pens, and pen physics

Wire finger drawing on PDF without breaking pinch; auto-hide page scrubber and fix bounce; share sticky tools with resize and per-page remember; side-button select; separate pen slots with colors; rnote pressure shapes plus tip-velocity width and lower stroke latency.

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

lib/editor/canvas/pen_note_screen.dart

@@ -470,12 +470,25 @@ class _PenNoteScreenState extends ConsumerState<PenNoteScreen> {
           eraserRadius: _penConfig?.value.eraserRadius ?? kDefaultEraserRadius,
           eraserWholeStroke: _penConfig?.value.eraserWholeStroke ?? false,
           sideButtonAction:
-              _penConfig?.value.sideButton ?? PenButtonAction.eraser,
+              _penConfig?.value.sideButton ?? PenButtonAction.select,
           eraserEndAction:
               _penConfig?.value.eraserEnd ?? PenButtonAction.eraser,
           allowFingerDrawing: _allowFingerDrawing,
           onStrokeComplete: _commitStroke,
           onEraseStroke: _eraseStroke,
+          onPenButtonAction: (action) {
+            if (action == PenButtonAction.select) {
+              setState(() => _tool = EditorToolKind.select);
+            } else if (action == PenButtonAction.undo) {
+              if (_undo.isNotEmpty) _performUndo();
+            } else if (action == PenButtonAction.toggleTool) {
+              setState(() {
+                _tool = _tool == EditorToolKind.eraser
+                    ? EditorToolKind.brush
+                    : EditorToolKind.eraser;
+              });
+            }
+          },
           // A white sheet with a soft shadow — the note "paper" — overlaid with
           // the selected background template, painted in page-pixel space (so it
           // scales with zoom) and BEHIND the ink layers.
@@ -510,19 +523,18 @@ class _PenNoteScreenState extends ConsumerState<PenNoteScreen> {
         child: Row(
           mainAxisSize: MainAxisSize.min,
           children: [
-            // Pen tool with brush picker (fountain / ballpoint / pencil), each
-            // brush showing its own remembered color.
-            BrushPickerButton(
-              selected: _penBrush,
-              active: _tool == EditorToolKind.brush,
-              tooltip: 'Brush',
-              labelFor: brushLabelEn,
-              colorFor: (b) => _brushColors[b] ?? Colors.black,
-              onSelected: (b) => setState(() {
-                _penBrush = b;
-                _tool = EditorToolKind.brush;
-              }),
-            ),
+            // OneNote-style: each pen is its own slot with remembered color.
+            for (final b in kPenToolBrushes)
+              PenSlotButton(
+                kind: b,
+                selected: _tool == EditorToolKind.brush && _penBrush == b,
+                color: _brushColors[b] ?? Colors.black,
+                tooltip: brushLabelEn(b),
+                onPressed: () => setState(() {
+                  _penBrush = b;
+                  _tool = EditorToolKind.brush;
+                }),
+              ),
             ToolButton(
               icon: Icons.brush_outlined,
               selected: _tool == EditorToolKind.highlighter,