feat(menu): delete category/item + fix RTL availability toggle

- Add DELETE /api/cafes/{cafeId}/menu/items/{id} (DeleteItemAsync soft-delete,
  mirroring the existing category delete) — item delete had no backend route.
- Dashboard menu admin: destructive "delete" action in the item and category
  edit modals, behind a shared confirm dialog (AlertDialog). Deleting the
  selected category falls back to "all items".
- Fix the availability ToggleSwitch in RTL: force dir="ltr" so the knob's
  translate-x stays inside the track instead of escaping on the right
  (same fix as the admin-panel toggles).
- i18n: deleteItem/deleteCategory confirm + success strings (fa/en/ar).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/dashboard/messages/fa.json

@@ -806,7 +806,13 @@
     "addItemSuccess": "آیتم اضافه شد",
     "updateItemSuccess": "آیتم به‌روز شد",
     "addCategorySuccess": "دسته اضافه شد",
-    "updateCategorySuccess": "دسته به‌روز شد"
+    "updateCategorySuccess": "دسته به‌روز شد",
+    "deleteItemConfirmTitle": "حذف آیتم",
+    "deleteItemConfirmDesc": "آیا از حذف «{name}» مطمئن هستید؟ این عمل قابل بازگشت نیست.",
+    "deleteItemSuccess": "آیتم حذف شد",
+    "deleteCategoryConfirmTitle": "حذف دسته‌بندی",
+    "deleteCategoryConfirmDesc": "آیا از حذف دسته «{name}» مطمئن هستید؟",
+    "deleteCategorySuccess": "دسته حذف شد"
   },
   "branchMenu": {
     "title": "منوی شعبه",