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>

src/app/api/admin/renders/[jobId]/stop/route.ts

@@ -0,0 +1,9 @@
+import { type NextRequest } from "next/server";
+import { adminProxy } from "@/app/api/admin/_adminProxy";
+
+export const runtime = "nodejs";
+interface Ctx { params: { jobId: string } }
+
+export async function POST(req: NextRequest, { params }: Ctx) {
+  return adminProxy(req, `/v1/renders/${params.jobId}/stop`);
+}