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/l10n/app_en.arb

@@ -237,5 +237,18 @@
   "@diagExported": { "placeholders": { "bytes": { "type": "int" } } },
   "diagExportFail": "Export failed: {error}",
   "@diagExportFail": { "placeholders": { "error": { "type": "String" } } },
-  "processingOcr": "Processing OCR…"
+  "processingOcr": "Processing OCR…",
+  "notebooksSection": "Notebooks",
+  "addBlankPage": "Blank page",
+  "importIntoNotebook": "Import into notebook",
+  "notebookMembersEmpty": "No pages yet",
+  "memberCount": "{count} items",
+  "@memberCount": {
+    "placeholders": { "count": { "type": "int" } }
+  },
+  "textFontSmall": "S",
+  "textFontMedium": "M",
+  "textFontLarge": "L",
+  "textBold": "Bold",
+  "textDragHint": "Drag to move"
 }