feat(render+admin): stop a render job (admin, any owner)

The render-queue cancel button used the owner-scoped /cancel (WHERE user_id=…),
so an admin couldn't stop another user's job. Added:
- render-svc: POST /v1/renders/:job_id/stop (admin-gated) → store.StopJob cancels
  any in-progress job regardless of owner and frees the assigned node
- admin: render-queue button now "توقف" → /api/admin/renders/{id}/stop (with confirm)

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

messages/en.json

@@ -415,7 +415,8 @@
       "colCreated": "Created",
       "colActions": "Actions",
       "actionRetry": "Retry",
-      "actionCancel": "Cancel"
+      "actionCancel": "Cancel",
+      "actionStop": "Stop"
     },
     "componentsAuthAuthPageContent": {
       "genericError": "Something went wrong. Please try again.",

messages/fa.json

@@ -415,7 +415,8 @@
       "colCreated": "زمان ایجاد",
       "colActions": "عملیات",
       "actionRetry": "تلاش مجدد",
-      "actionCancel": "لغو"
+      "actionCancel": "لغو",
+      "actionStop": "توقف"
     },
     "componentsAuthAuthPageContent": {
       "genericError": "خطایی رخ داد. لطفاً دوباره تلاش کنید.",