feat(app): block selecting already-uploaded photos at picker tap (double-tap to force)

方案 A（选图点选拦截）：multiImagePickerProvider 经 wechat_assets_picker
10.1.3 官方钩子 AssetPickerConfig.selectPredicate 挂 PickerDuplicateGate——
点选「已上传到目标相册」的照片当场拦下（SnackBar 提示），再次点击同一张
强制选择（escape hatch）。

- MultiImagePicker typedef 增参 accountId/albumId（拦截判定范围=当前
  目标相册；相册详情/连拍页两处调用点传入）；
- 判定口径同 checkDuplicatesUnified：本机 TaskStore（同账号+相册+
  completed，filename+bytes）∪ 服务器单项预检（bytes；本机命中短路
  服务器，点选延迟考量）；任一半场异常按该半场无命中，fileSize 失败等
  整体异常直接放行——enqueue 弹窗 + init 409 兜底不变；
- per-asset 判定缓存（二次点击瞬回）+ 二次点击放行集；取消选择恒放行
  且不预热放行集；
- AssetEntity 事实适配（PickerAssetFact 测试接缝）：fileSize 为
  photo_manager 3.12 的 Future<int> 平台通道 getter（entity.dart:778），
  惰性求值；title 为 String?（Android 恒有值；iOS 需 needTitle——null
  时本机半场跳过，服务器按 bytes 仍可判）；
- l10n pickerDuplicateBlocked（zh/en）；测试替身签名同步
  （album_detail/capture_page 页测 + integration_test app_boot），
  页测补 (accountId, albumId) 接线断言；gate 五态用例入 enqueue_test。

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

apps/mobile/lib/l10n/app_en.arb

@@ -349,6 +349,7 @@
     }
   },
   "uploadPickNone": "No photos selected",
+  "pickerDuplicateBlocked": "Already uploaded to this album — tap again to select anyway",
   "albumManagePhotos": "Manage photos",
   "albumTakeFirstPhoto": "Take the first photo",
   "albumUploadDisabledHint": "Uploads are off for this album. New photos cannot be added right now",

apps/mobile/lib/l10n/app_localizations.dart

@@ -1688,6 +1688,12 @@ abstract class AppLocalizations {
   /// **'未选择照片'**
   String get uploadPickNone;
 
+  /// No description provided for @pickerDuplicateBlocked.
+  ///
+  /// In zh, this message translates to:
+  /// **'这张已上传到该相册——再点一次可强制选择'**
+  String get pickerDuplicateBlocked;
+
   /// No description provided for @albumManagePhotos.
   ///
   /// In zh, this message translates to:

apps/mobile/lib/l10n/app_localizations_en.dart

@@ -856,6 +856,10 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get uploadPickNone => 'No photos selected';
 
+  @override
+  String get pickerDuplicateBlocked =>
+      'Already uploaded to this album — tap again to select anyway';
+
   @override
   String get albumManagePhotos => 'Manage photos';
 

apps/mobile/lib/l10n/app_localizations_zh.dart

@@ -828,6 +828,9 @@ class AppLocalizationsZh extends AppLocalizations {
   @override
   String get uploadPickNone => '未选择照片';
 
+  @override
+  String get pickerDuplicateBlocked => '这张已上传到该相册——再点一次可强制选择';
+
   @override
   String get albumManagePhotos => '管理照片';
 

apps/mobile/lib/l10n/app_zh.arb

@@ -349,6 +349,7 @@
     }
   },
   "uploadPickNone": "未选择照片",
+  "pickerDuplicateBlocked": "这张已上传到该相册——再点一次可强制选择",
   "albumManagePhotos": "管理照片",
   "albumTakeFirstPhoto": "拍摄第一张照片",
   "albumUploadDisabledHint": "相册已关闭上传，暂不能新增照片",