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/migrations/001_initial_schema.sql

@@ -398,14 +398,9 @@ CREATE TABLE meal_diary (
     user_id    UUID          NOT NULL REFERENCES users(id)   ON DELETE CASCADE,
     date       DATE          NOT NULL,
     meal_type  TEXT          NOT NULL,
-    name       TEXT          NOT NULL,
     portions   DECIMAL(5,2)  NOT NULL DEFAULT 1,
-    calories   DECIMAL(8,2),
-    protein_g  DECIMAL(8,2),
-    fat_g      DECIMAL(8,2),
-    carbs_g    DECIMAL(8,2),
     source     TEXT          NOT NULL DEFAULT 'manual',
-    dish_id    UUID          REFERENCES dishes(id)   ON DELETE SET NULL,
+    dish_id    UUID          NOT NULL REFERENCES dishes(id)   ON DELETE RESTRICT,
     recipe_id  UUID          REFERENCES recipes(id)  ON DELETE SET NULL,
     portion_g  DECIMAL(10,2),
     created_at TIMESTAMPTZ   NOT NULL DEFAULT now()