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_ja.arb

@@ -96,5 +96,11 @@
   "mealTypeSnack": "間食",
   "navHome": "ホーム",
   "navProducts": "食品",
-  "navRecipes": "レシピ"
+  "navRecipes": "レシピ",
+  "addFromReceiptOrPhoto": "レシートや写真から追加",
+  "chooseMethod": "方法を選択",
+  "photoReceipt": "レシートを撮影",
+  "photoReceiptSubtitle": "レシートから全商品を認識",
+  "photoProducts": "食品を撮影",
+  "photoProductsSubtitle": "冷蔵庫・テーブル・棚 — 最大3枚"
 }