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_en.arb

@@ -428,5 +428,6 @@
   "posterSaved": "Poster saved to gallery",
   "posterSaveFailed": "Failed to save poster",
   "close": "Close",
-  "albumUploadDisabled": "Upload is disabled for this album"
+  "albumUploadDisabled": "Upload is disabled for this album",
+  "networkOfflineBanner": "No network. Photos will upload automatically when reconnected."
 }