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/recipe/model.go

@@ -1,28 +1,18 @@
 package recipe
 
-import (
-	"encoding/json"
-	"time"
-)
+import "time"
 
-// Recipe is a recipe record in the database.
-// Title, Description, Ingredients, and Steps hold the content for the language
-// resolved at query time (English by default, or from recipe_translations when
-// a matching row exists for the requested language).
+// Recipe is a cooking variant of a Dish in the catalog.
+// It links to a Dish for all presentational data (name, image, cuisine, tags).
 type Recipe struct {
-	ID            string `json:"id"`
-	Source        string `json:"source"` // spoonacular | ai | user
-	SpoonacularID *int   `json:"spoonacular_id"`
+	ID     string `json:"id"`
+	DishID string `json:"dish_id"`
+	Source string `json:"source"` // ai | user | spoonacular
 
-	Title       string  `json:"title"`
-	Description *string `json:"description"`
-
-	Cuisine    *string `json:"cuisine"`
-	Difficulty *string `json:"difficulty"` // easy | medium | hard
-	PrepTimeMin *int   `json:"prep_time_min"`
-	CookTimeMin *int   `json:"cook_time_min"`
-	Servings    *int   `json:"servings"`
-	ImageURL    *string `json:"image_url"`
+	Difficulty  *string `json:"difficulty"`
+	PrepTimeMin *int    `json:"prep_time_min"`
+	CookTimeMin *int    `json:"cook_time_min"`
+	Servings    *int    `json:"servings"`
 
 	CaloriesPerServing *float64 `json:"calories_per_serving"`
 	ProteinPerServing  *float64 `json:"protein_per_serving"`
@@ -30,29 +20,29 @@ type Recipe struct {
 	CarbsPerServing    *float64 `json:"carbs_per_serving"`
 	FiberPerServing    *float64 `json:"fiber_per_serving"`
 
-	Ingredients json.RawMessage `json:"ingredients"` // []RecipeIngredient
-	Steps       json.RawMessage `json:"steps"`       // []RecipeStep
-	Tags        json.RawMessage `json:"tags"`        // []string
+	Ingredients []RecipeIngredient `json:"ingredients"`
+	Steps       []RecipeStep       `json:"steps"`
+	Notes       *string            `json:"notes,omitempty"`
 
-	AvgRating   float64   `json:"avg_rating"`
-	ReviewCount int       `json:"review_count"`
-	CreatedBy   *string   `json:"created_by"`
-	CreatedAt   time.Time `json:"created_at"`
-	UpdatedAt   time.Time `json:"updated_at"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
 }
 
-// RecipeIngredient is a single ingredient in a recipe's JSONB array.
+// RecipeIngredient is a single ingredient row from recipe_ingredients.
 type RecipeIngredient struct {
-	MappingID *string `json:"mapping_id"`
-	Name      string  `json:"name"`
-	Amount    float64 `json:"amount"`
-	Unit      string  `json:"unit"`
-	Optional  bool    `json:"optional"`
+	ID           string   `json:"id"`
+	IngredientID *string  `json:"ingredient_id"`
+	Name         string   `json:"name"`
+	Amount       float64  `json:"amount"`
+	UnitCode     *string  `json:"unit_code"`
+	IsOptional   bool     `json:"is_optional"`
+	SortOrder    int      `json:"sort_order"`
 }
 
-// RecipeStep is a single step in a recipe's JSONB array.
+// RecipeStep is a single step row from recipe_steps.
 type RecipeStep struct {
-	Number       int     `json:"number"`
+	ID           string  `json:"id"`
+	StepNumber   int     `json:"step_number"`
 	Description  string  `json:"description"`
 	TimerSeconds *int    `json:"timer_seconds"`
 	ImageURL     *string `json:"image_url"`