feat(i18n): localize settings + search screens

Extend the en/zh localization to the two screens reached from the home
app bar (the "全都用 + 多语言" ask):
- settings: title, theme-mode segments (System/Light/Dark), seed-color
  description, color-picker + clear-data dialogs.
- search: hint, error, empty/no-results states, Notes/Documents section
  headers, page label.

New ARB keys regenerated; l10n_test now asserts the new keys resolve in
both English and Chinese.

flutter analyze: 0 issues. l10n_test: 3/3.

lib/l10n/app_en.arb

@@ -15,6 +15,31 @@
   "openInSplitView": "Open in Split View",
   "splitViewSubtitle": "PDF reference + scratchpad",
   "removeDocument": "Remove document",
+  "ok": "OK",
+  "pickColor": "Pick a color",
+  "clearSettingsTitle": "Clear all local settings?",
+  "clear": "Clear",
+  "settingsReset": "Settings reset to defaults",
+  "themeSystem": "System",
+  "themeLight": "Light",
+  "themeDark": "Dark",
+  "seedColorDesc": "Seed color for Material 3 theme",
+  "searchHint": "Search notes and documents...",
+  "searchError": "Search error: {error}",
+  "@searchError": {
+    "placeholders": { "error": { "type": "String" } }
+  },
+  "noResultsFor": "No results for \"{query}\"",
+  "@noResultsFor": {
+    "placeholders": { "query": { "type": "String" } }
+  },
+  "typeToSearch": "Type to search your notes and documents",
+  "sectionNotes": "Notes",
+  "sectionDocuments": "Documents",
+  "pageLabel": "Page {page}",
+  "@pageLabel": {
+    "placeholders": { "page": { "type": "int" } }
+  },
   "processingPptx": "Processing PPTX...",
   "processingPresentation": "Processing presentation...",
   "couldNotOpenPresentation": "Could not open presentation.",

lib/l10n/app_localizations.dart

@@ -188,6 +188,102 @@ abstract class AppLocalizations {
   /// **'Remove document'**
   String get removeDocument;
 
+  /// No description provided for @ok.
+  ///
+  /// In en, this message translates to:
+  /// **'OK'**
+  String get ok;
+
+  /// No description provided for @pickColor.
+  ///
+  /// In en, this message translates to:
+  /// **'Pick a color'**
+  String get pickColor;
+
+  /// No description provided for @clearSettingsTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Clear all local settings?'**
+  String get clearSettingsTitle;
+
+  /// No description provided for @clear.
+  ///
+  /// In en, this message translates to:
+  /// **'Clear'**
+  String get clear;
+
+  /// No description provided for @settingsReset.
+  ///
+  /// In en, this message translates to:
+  /// **'Settings reset to defaults'**
+  String get settingsReset;
+
+  /// No description provided for @themeSystem.
+  ///
+  /// In en, this message translates to:
+  /// **'System'**
+  String get themeSystem;
+
+  /// No description provided for @themeLight.
+  ///
+  /// In en, this message translates to:
+  /// **'Light'**
+  String get themeLight;
+
+  /// No description provided for @themeDark.
+  ///
+  /// In en, this message translates to:
+  /// **'Dark'**
+  String get themeDark;
+
+  /// No description provided for @seedColorDesc.
+  ///
+  /// In en, this message translates to:
+  /// **'Seed color for Material 3 theme'**
+  String get seedColorDesc;
+
+  /// No description provided for @searchHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Search notes and documents...'**
+  String get searchHint;
+
+  /// No description provided for @searchError.
+  ///
+  /// In en, this message translates to:
+  /// **'Search error: {error}'**
+  String searchError(String error);
+
+  /// No description provided for @noResultsFor.
+  ///
+  /// In en, this message translates to:
+  /// **'No results for \"{query}\"'**
+  String noResultsFor(String query);
+
+  /// No description provided for @typeToSearch.
+  ///
+  /// In en, this message translates to:
+  /// **'Type to search your notes and documents'**
+  String get typeToSearch;
+
+  /// No description provided for @sectionNotes.
+  ///
+  /// In en, this message translates to:
+  /// **'Notes'**
+  String get sectionNotes;
+
+  /// No description provided for @sectionDocuments.
+  ///
+  /// In en, this message translates to:
+  /// **'Documents'**
+  String get sectionDocuments;
+
+  /// No description provided for @pageLabel.
+  ///
+  /// In en, this message translates to:
+  /// **'Page {page}'**
+  String pageLabel(int page);
+
   /// No description provided for @processingPptx.
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_en.dart

@@ -53,6 +53,60 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get removeDocument => 'Remove document';
 
+  @override
+  String get ok => 'OK';
+
+  @override
+  String get pickColor => 'Pick a color';
+
+  @override
+  String get clearSettingsTitle => 'Clear all local settings?';
+
+  @override
+  String get clear => 'Clear';
+
+  @override
+  String get settingsReset => 'Settings reset to defaults';
+
+  @override
+  String get themeSystem => 'System';
+
+  @override
+  String get themeLight => 'Light';
+
+  @override
+  String get themeDark => 'Dark';
+
+  @override
+  String get seedColorDesc => 'Seed color for Material 3 theme';
+
+  @override
+  String get searchHint => 'Search notes and documents...';
+
+  @override
+  String searchError(String error) {
+    return 'Search error: $error';
+  }
+
+  @override
+  String noResultsFor(String query) {
+    return 'No results for \"$query\"';
+  }
+
+  @override
+  String get typeToSearch => 'Type to search your notes and documents';
+
+  @override
+  String get sectionNotes => 'Notes';
+
+  @override
+  String get sectionDocuments => 'Documents';
+
+  @override
+  String pageLabel(int page) {
+    return 'Page $page';
+  }
+
   @override
   String get processingPptx => 'Processing PPTX...';
 

lib/l10n/app_localizations_zh.dart

@@ -53,6 +53,60 @@ class AppLocalizationsZh extends AppLocalizations {
   @override
   String get removeDocument => '移除文档';
 
+  @override
+  String get ok => '确定';
+
+  @override
+  String get pickColor => '选择颜色';
+
+  @override
+  String get clearSettingsTitle => '清除所有本地设置？';
+
+  @override
+  String get clear => '清除';
+
+  @override
+  String get settingsReset => '设置已恢复默认';
+
+  @override
+  String get themeSystem => '跟随系统';
+
+  @override
+  String get themeLight => '浅色';
+
+  @override
+  String get themeDark => '深色';
+
+  @override
+  String get seedColorDesc => 'Material 3 主题种子色';
+
+  @override
+  String get searchHint => '搜索笔记和文档…';
+
+  @override
+  String searchError(String error) {
+    return '搜索出错：$error';
+  }
+
+  @override
+  String noResultsFor(String query) {
+    return '没有“$query”的结果';
+  }
+
+  @override
+  String get typeToSearch => '输入以搜索你的笔记和文档';
+
+  @override
+  String get sectionNotes => '笔记';
+
+  @override
+  String get sectionDocuments => '文档';
+
+  @override
+  String pageLabel(int page) {
+    return '第 $page 页';
+  }
+
   @override
   String get processingPptx => '正在处理 PPTX…';
 

lib/l10n/app_zh.arb

@@ -15,6 +15,22 @@
   "openInSplitView": "分屏打开",
   "splitViewSubtitle": "PDF 参考 + 草稿纸",
   "removeDocument": "移除文档",
+  "ok": "确定",
+  "pickColor": "选择颜色",
+  "clearSettingsTitle": "清除所有本地设置？",
+  "clear": "清除",
+  "settingsReset": "设置已恢复默认",
+  "themeSystem": "跟随系统",
+  "themeLight": "浅色",
+  "themeDark": "深色",
+  "seedColorDesc": "Material 3 主题种子色",
+  "searchHint": "搜索笔记和文档…",
+  "searchError": "搜索出错：{error}",
+  "noResultsFor": "没有“{query}”的结果",
+  "typeToSearch": "输入以搜索你的笔记和文档",
+  "sectionNotes": "笔记",
+  "sectionDocuments": "文档",
+  "pageLabel": "第 {page} 页",
   "processingPptx": "正在处理 PPTX…",
   "processingPresentation": "正在处理演示文稿…",
   "couldNotOpenPresentation": "无法打开演示文稿。",