feat: localise scan screen (12 languages)

Replace all hardcoded Russian strings in ScanScreen and _LoadingDialog
with AppLocalizations keys; add addFromReceiptOrPhoto, chooseMethod,
photoReceipt, photoReceiptSubtitle, photoProducts, photoProductsSubtitle,
recognizing keys to all 12 ARB files and regenerate AppLocalizations.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/l10n/app_localizations_zh.dart

@@ -285,4 +285,22 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get navRecipes => '食谱';
+
+  @override
+  String get addFromReceiptOrPhoto => '从收据或照片添加';
+
+  @override
+  String get chooseMethod => '选择方式';
+
+  @override
+  String get photoReceipt => '拍摄收据';
+
+  @override
+  String get photoReceiptSubtitle => '识别收据中的所有商品';
+
+  @override
+  String get photoProducts => '拍摄食品';
+
+  @override
+  String get photoProductsSubtitle => '冰箱、桌子、货架 — 最多3张照片';
 }