feat: core schema redesign — dishes, structured recipes, cuisines, tags (iteration 7)

Replaces the flat JSONB-based recipe schema with a normalized relational model:

Schema (migrations consolidated to 001_initial_schema + 002_seed_data):
- New: dishes, dish_translations, dish_tags — canonical dish catalog
- New: cuisines, tags, dish_categories with _translations tables + full seed data
- New: recipe_ingredients, recipe_steps with _translations (replaces JSONB blobs)
- New: user_saved_recipes thin bookmark (drops saved_recipes + saved_recipe_translations)
- New: product_ingredients M2M table
- recipes: now a cooking variant of a dish (dish_id FK, no title/JSONB columns)
- recipe_translations: repurposed to per-language notes only
- products: mapping_id → primary_ingredient_id
- menu_items: recipe_id FK → recipes; adds dish_id
- meal_diary: adds dish_id, recipe_id → recipes, portion_g

Backend (Go):
- New packages: internal/cuisine, internal/tag, internal/dish (registry + handler + repo)
- New GET /cuisines, GET /tags (public), GET /dishes, GET /dishes/{id}, GET /recipes/{id}
- recipe, savedrecipe, menu, diary, product, ingredient packages updated for new schema

Flutter:
- New models: Cuisine, Tag; new providers: cuisineNamesProvider, tagNamesProvider
- recipe.dart: RecipeIngredient gains unit_code + effectiveUnit getter
- saved_recipe.dart: thin model, manual fromJson, computed nutrition getter
- diary_entry.dart: adds dishId, recipeId, portionG
- recipe_detail_screen.dart: localized cuisine/tag names via providers

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

backend/internal/product/repository.go

@@ -25,7 +25,7 @@ func NewRepository(pool *pgxpool.Pool) *Repository {
 
 // expires_at is computed in SQL because TIMESTAMPTZ + INTERVAL is STABLE (not IMMUTABLE),
 // which prevents it from being used as a stored generated column.
-const selectCols = `id, user_id, mapping_id, name, quantity, unit, category, storage_days, added_at,
+const selectCols = `id, user_id, primary_ingredient_id, name, quantity, unit, category, storage_days, added_at,
 	(added_at + storage_days * INTERVAL '1 day') AS expires_at`
 
 // List returns all products for a user, sorted by expires_at ASC.
@@ -57,11 +57,17 @@ func (r *Repository) Create(ctx context.Context, userID string, req CreateReques
 		qty = 1
 	}
 
+	// Accept both new and legacy field names.
+	primaryID := req.PrimaryIngredientID
+	if primaryID == nil {
+		primaryID = req.MappingID
+	}
+
 	row := r.pool.QueryRow(ctx, `
-		INSERT INTO products (user_id, mapping_id, name, quantity, unit, category, storage_days)
+		INSERT INTO products (user_id, primary_ingredient_id, name, quantity, unit, category, storage_days)
 		VALUES ($1, $2, $3, $4, $5, $6, $7)
 		RETURNING `+selectCols,
-		userID, req.MappingID, req.Name, qty, unit, req.Category, storageDays,
+		userID, primaryID, req.Name, qty, unit, req.Category, storageDays,
 	)
 	return scanProduct(row)
 }
@@ -144,11 +150,11 @@ func (r *Repository) ListForPrompt(ctx context.Context, userID string) ([]string
 		line := fmt.Sprintf("- %s %.0f %s", name, qty, unit)
 		switch {
 		case daysLeft <= 0:
-			line += " (истекает сегодня ⚠)"
+			line += " (expires today ⚠)"
 		case daysLeft == 1:
-			line += " (истекает завтра ⚠)"
+			line += " (expires tomorrow ⚠)"
 		case daysLeft <= 3:
-			line += fmt.Sprintf(" (истекает через %d дня ⚠)", daysLeft)
+			line += fmt.Sprintf(" (expires in %d days ⚠)", daysLeft)
 		}
 		lines = append(lines, line)
 	}
@@ -160,7 +166,7 @@ func (r *Repository) ListForPrompt(ctx context.Context, userID string) ([]string
 func scanProduct(row pgx.Row) (*Product, error) {
 	var p Product
 	err := row.Scan(
-		&p.ID, &p.UserID, &p.MappingID, &p.Name, &p.Quantity, &p.Unit,
+		&p.ID, &p.UserID, &p.PrimaryIngredientID, &p.Name, &p.Quantity, &p.Unit,
 		&p.Category, &p.StorageDays, &p.AddedAt, &p.ExpiresAt,
 	)
 	if err != nil {
@@ -175,7 +181,7 @@ func collectProducts(rows pgx.Rows) ([]*Product, error) {
 	for rows.Next() {
 		var p Product
 		if err := rows.Scan(
-			&p.ID, &p.UserID, &p.MappingID, &p.Name, &p.Quantity, &p.Unit,
+			&p.ID, &p.UserID, &p.PrimaryIngredientID, &p.Name, &p.Quantity, &p.Unit,
 			&p.Category, &p.StorageDays, &p.AddedAt, &p.ExpiresAt,
 		); err != nil {
 			return nil, fmt.Errorf("scan product: %w", err)