feat(app): crop cover & banner before upload (crop_your_image, 16:9 / 3:1)

review fixes: drop GIF from pre-sniff (package maps gif→png decode → never-ready hang); PopScope blocks back during processing

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

apps/mobile/lib/l10n/app_en.arb

@@ -429,5 +429,10 @@
   "posterSaveFailed": "Failed to save poster",
   "close": "Close",
   "albumUploadDisabled": "Upload is disabled for this album",
-  "networkOfflineBanner": "No network. Photos will upload automatically when reconnected."
+  "networkOfflineBanner": "No network. Photos will upload automatically when reconnected.",
+  "cropTitle": "Crop image",
+  "cropConfirm": "Done",
+  "cropCancel": "Cancel",
+  "cropProcessing": "Processing…",
+  "cropUnsupportedFormat": "This image format isn't supported yet — please pick JPG/PNG"
 }

apps/mobile/lib/l10n/app_localizations.dart

@@ -2029,6 +2029,36 @@ abstract class AppLocalizations {
   /// 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;
+
+  /// No description provided for @cropTitle.
+  ///
+  /// In zh, this message translates to:
+  /// **'裁剪图片'**
+  String get cropTitle;
+
+  /// No description provided for @cropConfirm.
+  ///
+  /// In zh, this message translates to:
+  /// **'完成'**
+  String get cropConfirm;
+
+  /// No description provided for @cropCancel.
+  ///
+  /// In zh, this message translates to:
+  /// **'取消'**
+  String get cropCancel;
+
+  /// No description provided for @cropProcessing.
+  ///
+  /// In zh, this message translates to:
+  /// **'处理中…'**
+  String get cropProcessing;
+
+  /// No description provided for @cropUnsupportedFormat.
+  ///
+  /// In zh, this message translates to:
+  /// **'暂不支持该图片格式，请选择 JPG/PNG'**
+  String get cropUnsupportedFormat;
 }
 
 class _AppLocalizationsDelegate

apps/mobile/lib/l10n/app_localizations_en.dart

@@ -1038,4 +1038,20 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get networkOfflineBanner =>
       'No network. Photos will upload automatically when reconnected.';
+
+  @override
+  String get cropTitle => 'Crop image';
+
+  @override
+  String get cropConfirm => 'Done';
+
+  @override
+  String get cropCancel => 'Cancel';
+
+  @override
+  String get cropProcessing => 'Processing…';
+
+  @override
+  String get cropUnsupportedFormat =>
+      'This image format isn\'t supported yet — please pick JPG/PNG';
 }

apps/mobile/lib/l10n/app_localizations_zh.dart

@@ -1004,4 +1004,19 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get networkOfflineBanner => '当前无网络连接，照片将在恢复后自动上传';
+
+  @override
+  String get cropTitle => '裁剪图片';
+
+  @override
+  String get cropConfirm => '完成';
+
+  @override
+  String get cropCancel => '取消';
+
+  @override
+  String get cropProcessing => '处理中…';
+
+  @override
+  String get cropUnsupportedFormat => '暂不支持该图片格式，请选择 JPG/PNG';
 }

apps/mobile/lib/l10n/app_zh.arb

@@ -429,5 +429,10 @@
   "posterSaveFailed": "海报保存失败",
   "close": "关闭",
   "albumUploadDisabled": "该相册已关闭上传，无法添加照片",
-  "networkOfflineBanner": "当前无网络连接，照片将在恢复后自动上传"
+  "networkOfflineBanner": "当前无网络连接，照片将在恢复后自动上传",
+  "cropTitle": "裁剪图片",
+  "cropConfirm": "完成",
+  "cropCancel": "取消",
+  "cropProcessing": "处理中…",
+  "cropUnsupportedFormat": "暂不支持该图片格式，请选择 JPG/PNG"
 }