fix(agent-jobs): add heartbeat cancel and stale recovery

packages/backend/convex/crons.ts

@@ -12,6 +12,12 @@ crons.interval(
     limit: 10,
   },
 );
+crons.interval(
+  'Recover stale agent jobs',
+  { minutes: 1 },
+  internal.agentJobs.recoverStaleJobs,
+  {},
+);
 /* Example cron jobs
 crons.cron(
   // Run at 7:00 AM CST / 8:00 AM CDT