refactor: migrate ingredient aliases/categories to dedicated tables, drop spoonacular_id

- migration 012: create ingredient_categories + ingredient_category_translations
  tables (7 slugs, Russian names); add ingredient_aliases (ingredient_id, lang,
  alias) with GIN trigram index; migrate aliases JSONB from ingredient_mappings
  and ingredient_translations; drop aliases columns and spoonacular_id; add
  UNIQUE (canonical_name) as conflict key
- ingredient/model: remove SpoonacularID, add CategoryName for localized display
- ingredient/repository: conflict on canonical_name; GetByID/Search join category
  translations and aliases lateral; new UpsertAliases (pgx batch),
  UpsertCategoryTranslation; remove GetBySpoonacularID; split scan helpers into
  scanMappingWrite / scanMappingRead
- gemini/recognition: add IngredientTranslation type; IngredientClassification
  now carries Translations []IngredientTranslation instead of CanonicalNameRu;
  update ClassifyIngredient prompt to English with structured translations array
- recognition/handler: update ingredientRepo interface; saveClassification uses
  UpsertAliases and iterates Translations
- recipe/model: remove SpoonacularID from RecipeIngredient
- integration tests: remove SpoonacularID fixtures, replace GetBySpoonacularID
  tests with GetByID, add UpsertAliases and UpsertCategoryTranslation tests
- Flutter: remove canonicalNameRu from IngredientMapping, add categoryName;
  displayName returns server-resolved canonicalName; regenerate .g.dart

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

backend/internal/recipe/model.go

@@ -43,12 +43,11 @@ type Recipe struct {
 
 // RecipeIngredient is a single ingredient in a recipe's JSONB array.
 type RecipeIngredient struct {
-	SpoonacularID *int    `json:"spoonacular_id"`
-	MappingID     *string `json:"mapping_id"`
-	Name          string  `json:"name"`
-	Amount        float64 `json:"amount"`
-	Unit          string  `json:"unit"`
-	Optional      bool    `json:"optional"`
+	MappingID *string `json:"mapping_id"`
+	Name      string  `json:"name"`
+	Amount    float64 `json:"amount"`
+	Unit      string  `json:"unit"`
+	Optional  bool    `json:"optional"`
 }
 
 // RecipeStep is a single step in a recipe's JSONB array.