feat: slim meal_diary — derive name and nutrition from dish/recipe

Remove denormalized columns (name, calories, protein_g, fat_g, carbs_g)
from meal_diary. Name is now resolved via JOIN with dishes/dish_translations;
macros are computed as recipe.*_per_serving * portions at query time.

- Add dish.Repository.FindOrCreateRecipe: finds or creates a minimal recipe
  stub seeded with AI-estimated macros
- recognition/handler: resolve recipe_id synchronously per candidate;
  simplify enrichDishInBackground to translations-only
- diary/handler: accept dish_id OR name; always resolve recipe_id via
  FindOrCreateRecipe before INSERT
- diary/entity: DishID is now non-nullable string; CreateRequest drops macros
- diary/repository: ListByDate and Create use JOIN to return computed macros
- ai/types: add RecipeID field to DishCandidate
- Update tests and wire_gen accordingly

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

backend/internal/domain/diary/entity.go

@@ -7,14 +7,14 @@ type Entry struct {
 	ID        string    `json:"id"`
 	Date      string    `json:"date"` // YYYY-MM-DD
 	MealType  string    `json:"meal_type"`
-	Name      string    `json:"name"`
+	Name      string    `json:"name"`           // from dishes JOIN
 	Portions  float64   `json:"portions"`
-	Calories  *float64  `json:"calories,omitempty"`
+	Calories  *float64  `json:"calories,omitempty"`  // recipe.calories_per_serving * portions
 	ProteinG  *float64  `json:"protein_g,omitempty"`
 	FatG      *float64  `json:"fat_g,omitempty"`
 	CarbsG    *float64  `json:"carbs_g,omitempty"`
 	Source    string    `json:"source"`
-	DishID    *string   `json:"dish_id,omitempty"`
+	DishID    string    `json:"dish_id"`
 	RecipeID  *string   `json:"recipe_id,omitempty"`
 	PortionG  *float64  `json:"portion_g,omitempty"`
 	CreatedAt time.Time `json:"created_at"`
@@ -24,12 +24,8 @@ type Entry struct {
 type CreateRequest struct {
 	Date     string   `json:"date"`
 	MealType string   `json:"meal_type"`
-	Name     string   `json:"name"`
+	Name     string   `json:"name"`     // input-only; used if DishID is nil
 	Portions float64  `json:"portions"`
-	Calories *float64 `json:"calories"`
-	ProteinG *float64 `json:"protein_g"`
-	FatG     *float64 `json:"fat_g"`
-	CarbsG   *float64 `json:"carbs_g"`
 	Source   string   `json:"source"`
 	DishID   *string  `json:"dish_id"`
 	RecipeID *string  `json:"recipe_id"`