feat: unified shell, diagnostics pack, native Office, sticky board

Make Surface remote debugging and classroom workflows viable: always-on
structured logs with one-click zip export, a single AppShell chrome,
OOXML PPTX/DOCX annotation without LibreOffice, and a first-class sticky
board. Also drop spike/legacy ink widgets and tighten pen feel
(predictor, PenInfoHistory, page-tile layer).

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

lib/l10n/app_localizations_zh.dart

@@ -300,6 +300,42 @@ class AppLocalizationsZh extends AppLocalizations {
     return '$current / $total';
   }
 
+  @override
+  String get libraryTab => '库';
+
+  @override
+  String get boardTab => '便利贴';
+
+  @override
+  String get shellTagline => '手写 · 批注 · 知识';
+
+  @override
+  String get notesSection => '笔记';
+
+  @override
+  String get documentsSection => '文档';
+
+  @override
+  String get emptyLibraryTitle => '还没有内容';
+
+  @override
+  String get emptyLibraryBody => '新建笔记，或导入 PDF / PPT / Word';
+
+  @override
+  String get diagnosticsSection => '诊断';
+
+  @override
+  String get diagnosticsExport => '导出诊断包';
+
+  @override
+  String get diagnosticsExportHint => '在 Surface 上复现问题后导出，发回给开发者分析';
+
+  @override
+  String get diagnosticsToggle => '输入诊断叠加层';
+
+  @override
+  String get penSettingsUnified => '笔与墨迹';
+
   @override
   String get board => '便利贴板';