feat(app): P0 batch 3 — offline detection with engine pause/resume + UI banner

P0-4 离线感知：
  - connectivity_plus → NetworkAvailability（online/offline/unknown）
  - engine_scope 三重绑定：有账号+有网 → start；任一失去 → stop（在途不中断）
  - 网络恢复 → start + onNetworkRestored（waitingNetwork 即时重试）
  - HomePage 顶部离线黄条（wifi_off + i18n 双语）

P0-5 更正：EXIF 方向已由服务端 sharp .rotate() 自动转正——v2 分析误报

397/397 全绿、analyze 0

Co-Authored-By: Claude Code <noreply@anthropic.com>

apps/mobile/lib/l10n/app_localizations.dart

@@ -2023,6 +2023,12 @@ abstract class AppLocalizations {
   /// In zh, this message translates to:
   /// **'该相册已关闭上传，无法添加照片'**
   String get albumUploadDisabled;
+
+  /// No description provided for @networkOfflineBanner.
+  ///
+  /// In zh, this message translates to:
+  /// **'当前无网络连接，照片将在恢复后自动上传'**
+  String get networkOfflineBanner;
 }
 
 class _AppLocalizationsDelegate