(release) Track worker heartbeat for running jobs

Record worker pid, host, claim time, and heartbeat metadata on running
backup jobs so operators can see which worker owns a run.

Refresh the heartbeat while rsync is active and reconcile stale running
runs when the worker heartbeat stops. Add a worker option to tune or
disable stale-run reconciliation.

Refs #11

src/pobsync_backend/tests/test_views.py

@@ -1373,6 +1373,29 @@ class ViewTests(TestCase):
         self.assertContains(response, "Cancel run")
         self.assertContains(response, reverse("cancel_run", args=[run.id]))
 
+    def test_run_detail_renders_worker_execution_metadata(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+        run = BackupRun.objects.create(
+            host=host,
+            status=BackupRun.Status.RUNNING,
+            result={
+                "execution": {
+                    "worker_host": "backup-01",
+                    "worker_pid": 4242,
+                    "heartbeat_at": "2026-05-21T10:30:00+00:00",
+                }
+            },
+        )
+
+        response = self.client.get(reverse("run_detail", args=[run.id]))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "Worker:")
+        self.assertContains(response, "backup-01")
+        self.assertContains(response, "pid 4242")
+        self.assertContains(response, "Worker heartbeat:")
+
     def test_cancel_run_marks_queued_run_cancelled(self) -> None:
         self.client.force_login(self.staff_user)
         host = HostConfig.objects.create(host="web-01", address="web-01.example.test")