feat: Flutter client localisation (12 languages)

Add flutter_localizations + intl, 12 ARB files (en/ru/es/de/fr/it/pt/zh/ja/ko/ar/hi),
replace all hardcoded Russian UI strings with AppLocalizations, detect system locale
on first launch, localise bottom nav bar labels, document rule in CLAUDE.md.

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

client/lib/l10n/app_ja.arb

@@ -0,0 +1,100 @@
+{
+  "@@locale": "ja",
+  "appTitle": "FoodAI",
+  "greetingMorning": "おはようございます",
+  "greetingAfternoon": "こんにちは",
+  "greetingEvening": "こんばんは",
+  "caloriesUnit": "kcal",
+  "gramsUnit": "g",
+  "goalLabel": "目標：",
+  "consumed": "摂取済み",
+  "remaining": "残り",
+  "exceeded": "超過",
+  "proteinLabel": "タンパク質",
+  "fatLabel": "脂質",
+  "carbsLabel": "炭水化物",
+  "today": "今日",
+  "yesterday": "昨日",
+  "mealsSection": "食事",
+  "addDish": "料理を追加",
+  "scanDish": "スキャン",
+  "menu": "メニュー",
+  "dishHistory": "料理履歴",
+  "recommendCook": "おすすめレシピ",
+  "camera": "カメラ",
+  "gallery": "ギャラリー",
+  "analyzingPhoto": "写真を分析中...",
+  "inQueue": "順番待ち中",
+  "queuePosition": "{position}番目",
+  "@queuePosition": {
+    "placeholders": {
+      "position": { "type": "int" }
+    }
+  },
+  "processing": "処理中...",
+  "upgradePrompt": "順番をスキップ？アップグレード →",
+  "recognitionFailed": "認識に失敗しました。もう一度お試しください。",
+  "dishRecognition": "料理認識",
+  "all": "すべて",
+  "dishRecognized": "料理を認識しました",
+  "recognizing": "認識中…",
+  "recognitionError": "認識エラー",
+  "dishResultTitle": "料理を認識しました",
+  "selectDish": "料理を選択",
+  "dishNotRecognized": "料理を認識できませんでした",
+  "tryAgain": "もう一度試す",
+  "nutritionApproximate": "栄養値は概算です — 写真から推定されました。",
+  "portion": "量",
+  "mealType": "食事タイプ",
+  "dateLabel": "日付",
+  "addToJournal": "日記に追加",
+  "addFailed": "追加に失敗しました。もう一度お試しください。",
+  "historyTitle": "認識履歴",
+  "historyLoadError": "履歴の読み込みに失敗しました",
+  "retry": "再試行",
+  "noHistory": "認識履歴がありません",
+  "profileTitle": "プロフィール",
+  "edit": "編集",
+  "bodyParams": "身体パラメータ",
+  "goalActivity": "目標 & 活動",
+  "nutrition": "栄養",
+  "settings": "設定",
+  "height": "身長",
+  "weight": "体重",
+  "age": "年齢",
+  "gender": "性別",
+  "genderMale": "男性",
+  "genderFemale": "女性",
+  "goalLoss": "体重減少",
+  "goalMaintain": "維持",
+  "goalGain": "筋肉増量",
+  "activityLow": "低い",
+  "activityMedium": "普通",
+  "activityHigh": "高い",
+  "calorieGoal": "カロリー目標",
+  "mealTypes": "食事タイプ",
+  "formulaNote": "ミフリン・セントジョー式で計算",
+  "language": "言語",
+  "notSet": "未設定",
+  "calorieHint": "カロリー目標を計算するために身体パラメータを入力してください",
+  "logout": "ログアウト",
+  "editProfile": "プロフィールを編集",
+  "cancel": "キャンセル",
+  "save": "保存",
+  "nameLabel": "名前",
+  "heightCm": "身長（cm）",
+  "weightKg": "体重（kg）",
+  "birthDate": "生年月日",
+  "nameRequired": "名前を入力してください",
+  "profileUpdated": "プロフィールを更新しました",
+  "profileSaveFailed": "保存に失敗しました",
+  "mealTypeBreakfast": "朝食",
+  "mealTypeSecondBreakfast": "第二朝食",
+  "mealTypeLunch": "昼食",
+  "mealTypeAfternoonSnack": "おやつ",
+  "mealTypeDinner": "夕食",
+  "mealTypeSnack": "間食",
+  "navHome": "ホーム",
+  "navProducts": "食品",
+  "navRecipes": "レシピ"
+}