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_localizations_fr.dart

@@ -307,4 +307,22 @@ class AppLocalizationsFr extends AppLocalizations {
   @override
   String get photoProductsSubtitle =>
       'Réfrigérateur, table, étagère — jusqu\'à 3 photos';
+
+  @override
+  String get addPackagedFood => 'Ajouter un aliment emballé';
+
+  @override
+  String get scanBarcode => 'Scanner le code-barres';
+
+  @override
+  String get portionWeightG => 'Poids de la portion (g)';
+
+  @override
+  String get productNotFound => 'Produit introuvable';
+
+  @override
+  String get enterManually => 'Saisir manuellement';
+
+  @override
+  String get perHundredG => 'pour 100 g';
 }