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/editor/canvas/pen_slide_screen.dart

@@ -22,6 +22,7 @@ import '../input/pen_input_service.dart';
 import '../input/pressure_curve.dart' show kNaturalPressureGamma;
 import '../layout/viewport_fit.dart';
 import '../pdf/slide_export.dart';
+import '../ui/page_nav_shortcuts.dart';
 import '../ui/pen_settings_page.dart';
 import 'editor_tool.dart';
 import 'pen_canvas.dart';
@@ -335,7 +336,15 @@ class _PenSlideScreenState extends State<PenSlideScreen> {
   @override
   Widget build(BuildContext context) {
     final cs = Theme.of(context).colorScheme;
-    return Scaffold(
+    return pageNavShortcuts(
+      onPrevious:
+          _slideIndex > 0 ? () => _goToSlide(_slideIndex - 1) : null,
+      onNext: _slideIndex < _slideCount - 1
+          ? () => _goToSlide(_slideIndex + 1)
+          : null,
+      onFirst: _slideCount > 0 ? () => _goToSlide(0) : null,
+      onLast: _slideCount > 0 ? () => _goToSlide(_slideCount - 1) : null,
+      child: Scaffold(
       body: Stack(
         children: [
           Positioned.fill(child: _buildCanvas()),
@@ -383,6 +392,7 @@ class _PenSlideScreenState extends State<PenSlideScreen> {
             ),
         ],
       ),
+      ),
     );
   }