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/diary/repository.go

@@ -27,7 +27,7 @@ func (r *Repository) ListByDate(ctx context.Context, userID, date string) ([]*En
 	rows, err := r.pool.Query(ctx, `
 		SELECT id, date::text, meal_type, name, portions,
 		       calories, protein_g, fat_g, carbs_g,
-		       source, recipe_id, created_at
+		       source, dish_id, recipe_id, portion_g, created_at
 		FROM meal_diary
 		WHERE user_id = $1 AND date = $2::date
 		ORDER BY created_at ASC`, userID, date)
@@ -60,13 +60,13 @@ func (r *Repository) Create(ctx context.Context, userID string, req CreateReques
 
 	row := r.pool.QueryRow(ctx, `
 		INSERT INTO meal_diary (user_id, date, meal_type, name, portions,
-		    calories, protein_g, fat_g, carbs_g, source, recipe_id)
-		VALUES ($1, $2::date, $3, $4, $5, $6, $7, $8, $9, $10, $11)
+		    calories, protein_g, fat_g, carbs_g, source, dish_id, recipe_id, portion_g)
+		VALUES ($1, $2::date, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13)
 		RETURNING id, date::text, meal_type, name, portions,
-		    calories, protein_g, fat_g, carbs_g, source, recipe_id, created_at`,
+		    calories, protein_g, fat_g, carbs_g, source, dish_id, recipe_id, portion_g, created_at`,
 		userID, req.Date, req.MealType, req.Name, portions,
 		req.Calories, req.ProteinG, req.FatG, req.CarbsG,
-		source, req.RecipeID,
+		source, req.DishID, req.RecipeID, req.PortionG,
 	)
 	return scanEntry(row)
 }
@@ -95,7 +95,7 @@ func scanEntry(s scannable) (*Entry, error) {
 	err := s.Scan(
 		&e.ID, &e.Date, &e.MealType, &e.Name, &e.Portions,
 		&e.Calories, &e.ProteinG, &e.FatG, &e.CarbsG,
-		&e.Source, &e.RecipeID, &e.CreatedAt,
+		&e.Source, &e.DishID, &e.RecipeID, &e.PortionG, &e.CreatedAt,
 	)
 	if errors.Is(err, pgx.ErrNoRows) {
 		return nil, ErrNotFound