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/savedrecipe/model.go

@@ -1,43 +1,76 @@
 package savedrecipe
 
-import (
-	"encoding/json"
-	"time"
-)
+import "time"
 
-// SavedRecipe is a recipe saved by a specific user.
-type SavedRecipe struct {
-	ID          string          `json:"id"`
-	UserID      string          `json:"-"`
-	Title       string          `json:"title"`
-	Description *string         `json:"description"`
-	Cuisine     *string         `json:"cuisine"`
-	Difficulty  *string         `json:"difficulty"`
-	PrepTimeMin *int            `json:"prep_time_min"`
-	CookTimeMin *int            `json:"cook_time_min"`
-	Servings    *int            `json:"servings"`
-	ImageURL    *string         `json:"image_url"`
-	Ingredients json.RawMessage `json:"ingredients"`
-	Steps       json.RawMessage `json:"steps"`
-	Tags        json.RawMessage `json:"tags"`
-	Nutrition   json.RawMessage `json:"nutrition_per_serving"`
-	Source      string          `json:"source"`
-	SavedAt     time.Time       `json:"saved_at"`
+// UserSavedRecipe is a user's bookmark referencing a catalog recipe.
+// Display fields are populated by joining dishes + recipes.
+type UserSavedRecipe struct {
+	ID       string    `json:"id"`
+	UserID   string    `json:"-"`
+	RecipeID string    `json:"recipe_id"`
+	SavedAt  time.Time `json:"saved_at"`
+
+	// Display data — joined from dishes + recipes.
+	DishName    string   `json:"title"`        // dish name used as display title
+	Description *string  `json:"description"`
+	ImageURL    *string  `json:"image_url"`
+	CuisineSlug *string  `json:"cuisine_slug"`
+	Tags        []string `json:"tags"`
+
+	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"`
+	FatPerServing      *float64 `json:"fat_per_serving"`
+	CarbsPerServing    *float64 `json:"carbs_per_serving"`
+
+	Ingredients []RecipeIngredient `json:"ingredients"`
+	Steps       []RecipeStep       `json:"steps"`
+}
+
+// RecipeIngredient is a single ingredient row.
+type RecipeIngredient struct {
+	Name       string  `json:"name"`
+	Amount     float64 `json:"amount"`
+	UnitCode   *string `json:"unit_code"`
+	IsOptional bool    `json:"is_optional"`
+}
+
+// RecipeStep is a single step row.
+type RecipeStep struct {
+	StepNumber   int    `json:"number"`
+	Description  string `json:"description"`
+	TimerSeconds *int   `json:"timer_seconds"`
 }
 
 // SaveRequest is the body for POST /saved-recipes.
+// When recipe_id is provided, the existing catalog recipe is bookmarked.
+// Otherwise a new dish+recipe is created from the supplied fields.
 type SaveRequest struct {
-	Title       string          `json:"title"`
-	Description string          `json:"description"`
-	Cuisine     string          `json:"cuisine"`
-	Difficulty  string          `json:"difficulty"`
-	PrepTimeMin int             `json:"prep_time_min"`
-	CookTimeMin int             `json:"cook_time_min"`
-	Servings    int             `json:"servings"`
-	ImageURL    string          `json:"image_url"`
-	Ingredients json.RawMessage `json:"ingredients"`
-	Steps       json.RawMessage `json:"steps"`
-	Tags        json.RawMessage `json:"tags"`
-	Nutrition   json.RawMessage `json:"nutrition_per_serving"`
-	Source      string          `json:"source"`
+	RecipeID    string `json:"recipe_id"`     // optional: bookmark existing recipe
+	Title       string `json:"title"`
+	Description string `json:"description"`
+	Cuisine     string `json:"cuisine"`
+	Difficulty  string `json:"difficulty"`
+	PrepTimeMin int    `json:"prep_time_min"`
+	CookTimeMin int    `json:"cook_time_min"`
+	Servings    int    `json:"servings"`
+	ImageURL    string `json:"image_url"`
+	// Ingredients / Steps / Tags / Nutrition are JSONB for backward compatibility
+	// with the recommendation flow that sends the full Gemini response.
+	Ingredients interface{} `json:"ingredients"`
+	Steps       interface{} `json:"steps"`
+	Tags        interface{} `json:"tags"`
+	Nutrition   interface{} `json:"nutrition_per_serving"`
+	Source      string      `json:"source"`
 }
+
+// ErrNotFound is returned when a saved recipe does not exist for the given user.
+var ErrNotFound = errorString("saved recipe not found")
+
+type errorString string
+
+func (e errorString) Error() string { return string(e) }