feat: rename ingredients→products, products→user_products; add barcode/OFF import

- Rename catalog: ingredient/* → product/* (canonical_name, barcode, nutrition per 100g)
- Rename pantry: product/* → userproduct/* (user-owned items with expiry)
- Squash migrations into single 001_initial_schema.sql (clean-db baseline)
- product_categories: add English canonical name column; fix COALESCE in queries
- Remove product_translations: product names are stored in their original language
- Add default_unit_name to product API responses via unit_translations JOIN
- Add cmd/importoff: bulk import from OpenFoodFacts JSONL dump (COPY + ON CONFLICT)
- Diary: support product_id entries alongside dish_id (CHECK num_nonnulls = 1)
- Home: getLoggedCalories joins both recipes and catalog products
- Flutter: rename models/providers/services to match backend rename
- Flutter: add barcode scan flow for diary (mobile_scanner, product_portion_sheet)
- Flutter: localise 6 new keys across 12 languages (barcode scan, portion weight)
- Routes: GET /products/search, GET /products/barcode/{barcode}, /user-products

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

client/lib/l10n/app_ja.arb

@@ -28,7 +28,9 @@
   "queuePosition": "{position}番目",
   "@queuePosition": {
     "placeholders": {
-      "position": { "type": "int" }
+      "position": {
+        "type": "int"
+      }
     }
   },
   "processing": "処理中...",
@@ -102,5 +104,11 @@
   "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"
+  "photoProductsSubtitle": "冷蔵庫・テーブル・棚 — 最大3枚",
+  "addPackagedFood": "パッケージ食品を追加",
+  "scanBarcode": "バーコードをスキャン",
+  "portionWeightG": "1食分の重さ（g）",
+  "productNotFound": "商品が見つかりません",
+  "enterManually": "手動で入力",
+  "perHundredG": "100gあたり"
 }