feat(3d): meal-box merge, stored mutations, undo, mobile undo UI + i18n ×12

- Merge leftovers into existing meal_box when same recipeId + cookedAt date + frozen + available.
- Store mealBoxMutations JSONB on cooking_sessions for deterministic undo.
- Undo decrements portions/remaining, discards box at zero, appends correction ledger rows.
- Mobile: undo button in cooking/[id].tsx after-flow and meal-boxes.tsx within 24h window.
- i18n undo strings across all 12 locales; parity test green.
- 6 new integration tests: merge, no cross-date merge, frozen split, undo restore, undo discard, ledger invariant.
- Update FAS3 audit doc with 3d semantics.

Closes Fas 3d

packages/database/src/schema/meals.ts

@@ -74,6 +74,7 @@ export const mealBoxes = pgTable(
       .references(() => storageLocations.id),
     frozen: boolean("frozen").notNull().default(false),
     recommendedUseBy: date("recommended_use_by").notNull(),
+    leftoverSource: text("leftover_source"),
     reservedForUserId: uuid("reserved_for_user_id").references(() => users.id, {
       onDelete: "set null",
     }),