fix: show dish calories in search and fix portion sheet layout crash

- DishSearchResult now carries calories_per_serving (backend entity + repo
  LEFT JOIN recipes / MIN / GROUP BY; Flutter model + fromJson)
- _FoodTile.fromDish shows kcal/serving subtitle when available
- _DishPortionSheet quick-select buttons: Row → Wrap to avoid
  BoxConstraints infinite-width crash inside DraggableScrollableSheet

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

backend/internal/domain/dish/entity.go

@@ -61,10 +61,11 @@ type RecipeStep struct {
 
 // DishSearchResult is a lightweight dish returned by the search endpoint.
 type DishSearchResult struct {
-	ID       string   `json:"id"`
-	Name     string   `json:"name"`
-	ImageURL *string  `json:"image_url,omitempty"`
-	AvgRating float64 `json:"avg_rating"`
+	ID                 string   `json:"id"`
+	Name               string   `json:"name"`
+	ImageURL           *string  `json:"image_url,omitempty"`
+	AvgRating          float64  `json:"avg_rating"`
+	CaloriesPerServing *float64 `json:"calories_per_serving,omitempty"`
 }
 
 // CreateRequest is the body used to create a new dish + recipe at once.