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/adapters/ai/types.go

@@ -96,6 +96,8 @@ type ReceiptResult struct {
 
 // DishCandidate is a single dish recognition candidate with estimated nutrition.
 type DishCandidate struct {
+	DishID      *string `json:"dish_id,omitempty"`
+	RecipeID    *string `json:"recipe_id,omitempty"`
 	DishName    string  `json:"dish_name"`
 	WeightGrams int     `json:"weight_grams"`
 	Calories    float64 `json:"calories"`