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/ar.json

@@ -763,7 +763,13 @@
     "addItemSuccess": "تمت إضافة الصنف",
     "updateItemSuccess": "تم تحديث الصنف",
     "addCategorySuccess": "تمت إضافة الفئة",
-    "updateCategorySuccess": "تم تحديث الفئة"
+    "updateCategorySuccess": "تم تحديث الفئة",
+    "deleteItemConfirmTitle": "حذف الصنف",
+    "deleteItemConfirmDesc": "هل أنت متأكد من حذف «{name}»؟ لا يمكن التراجع عن هذا الإجراء.",
+    "deleteItemSuccess": "تم حذف الصنف",
+    "deleteCategoryConfirmTitle": "حذف الفئة",
+    "deleteCategoryConfirmDesc": "هل أنت متأكد من حذف الفئة «{name}»؟",
+    "deleteCategorySuccess": "تم حذف الفئة"
   },
   "branchMenu": {
     "title": "قائمة الفرع",