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

infrastructure/migrations/0017_cooking_sessions_meal_date.sql

@@ -0,0 +1,7 @@
+-- Fas 3d: spara måltidsdatum på cooking session för att kunna hitta
+-- matlådor som skapades/utökades vid samma tillfälle vid undo.
+ALTER TABLE cooking_sessions ADD COLUMN IF NOT EXISTS meal_date DATE;
+-- Bakåtfyll: använd completedAt-datumet för befintliga completed-sessioner.
+UPDATE cooking_sessions SET meal_date = completed_at::DATE WHERE meal_date IS NULL AND completed_at IS NOT NULL;
+UPDATE cooking_sessions SET meal_date = started_at::DATE WHERE meal_date IS NULL AND started_at IS NOT NULL;
+UPDATE cooking_sessions SET meal_date = created_at::DATE WHERE meal_date IS NULL;