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/pubspec.lock

@@ -193,6 +193,22 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.19.1"
+  connectivity_plus:
+    dependency: "direct main"
+    description:
+      name: connectivity_plus
+      sha256: "762c99f890ca8bf87f7337236f99edd42793843bc6c3631da294a76653a54bd0"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "7.3.1"
+  connectivity_plus_platform_interface:
+    dependency: transitive
+    description:
+      name: connectivity_plus_platform_interface
+      sha256: "3c09627c536d22fd24691a905cdd8b14520de69da52c7a97499c8be5284a32ed"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "2.1.0"
   convert:
     dependency: transitive
     description:
@@ -225,6 +241,14 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "3.1.9"
+  dbus:
+    dependency: transitive
+    description:
+      name: dbus
+      sha256: a48d5da28e89bd02196e80d81ed8d7954923d00a0f4a68cc20b575038f023383
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "0.7.15"
   dio:
     dependency: "direct main"
     description:
@@ -716,6 +740,14 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.19.2"
+  nm:
+    dependency: transitive
+    description:
+      name: nm
+      sha256: "2c9aae4127bdc8993206464fcc063611e0e36e72018696cd9631023a31b24254"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "0.5.0"
   objective_c:
     dependency: transitive
     description:
@@ -788,6 +820,14 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.3.0"
+  petitparser:
+    dependency: transitive
+    description:
+      name: petitparser
+      sha256: "91bd59303e9f769f108f8df05e371341b15d59e995e6806aefab827b58336675"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "7.0.2"
   platform:
     dependency: transitive
     description:
@@ -1241,6 +1281,14 @@ packages:
       url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.1.0"
+  xml:
+    dependency: transitive
+    description:
+      name: xml
+      sha256: "67f0aff7be013d107995e9b75bf4e7f2c3ef2dfdb2c8e68024bba0a7fd5756a4"
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "7.0.1"
   yaml:
     dependency: transitive
     description: