feat: food search sheet with FTS+trgm, dish/recent endpoints, multilingual aliases

Backend:
- GET /dishes/search — hybrid FTS (english + simple) + trgm + ILIKE search
- GET /diary/recent — recently used dishes and products for the current user
- product search upgraded: FTS on canonical_name and product_aliases, ranked by GREATEST(ts_rank, similarity)
- importoff: collect product_name_ru/de/fr/... as product_aliases for multilingual search (e.g. "сникерс" → "Snickers")
- migrations: FTS + trgm indexes merged into 001_initial_schema.sql (002 removed)

Flutter:
- FoodSearchSheet: debounced search field, recently-used section, product/dish results, scan-photo and barcode chips
- DishPortionSheet: quick ½/1/1½/2 buttons + custom input
- + button in meal card now opens FoodSearchSheet instead of going directly to AI scan
- 7 new l10n keys across all 12 languages

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

backend/internal/domain/dish/entity.go

@@ -59,6 +59,14 @@ type RecipeStep struct {
 	ImageURL     *string `json:"image_url"`
 }
 
+// DishSearchResult is a lightweight dish returned by the search endpoint.
+type DishSearchResult struct {
+	ID       string   `json:"id"`
+	Name     string   `json:"name"`
+	ImageURL *string  `json:"image_url,omitempty"`
+	AvgRating float64 `json:"avg_rating"`
+}
+
 // CreateRequest is the body used to create a new dish + recipe at once.
 // Used when saving a Gemini-generated recommendation.
 type CreateRequest struct {