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>

test/badnote_sidecar_test.dart

@@ -290,6 +290,24 @@ void main() {
     expect(t.text, '');
     expect(t.fontSize, 0.03);
     expect(t.color, 0xFF000000);
+    expect(t.fontWeight, 400);
+    expect(t.fontFamily, isNull);
+  });
+
+  test('SidecarText fontWeight and fontFamily round-trip', () {
+    const tx = SidecarText(
+      id: 't-bold',
+      nx: 0.1,
+      ny: 0.2,
+      text: '粗体',
+      fontSize: 0.045,
+      fontWeight: 700,
+      fontFamily: 'IBM Plex Sans',
+    );
+    final decoded = SidecarText.fromJson(tx.toJson());
+    expect(decoded, tx);
+    expect(decoded.fontWeight, 700);
+    expect(decoded.fontFamily, 'IBM Plex Sans');
   });
 
   test('paragraph-anchored bookmark round-trips its anchor + char index', () {