(feature) Link rsync logs from backup run detail

Record the final rsync log path for successful real backup runs, matching
the existing dry-run and failure result payloads.

Add a staff-only run log endpoint and surface the link on run detail pages,
including fallback log discovery for older runs based on snapshot_path.

Cover direct log links and inferred scheduled backup logs with view tests.

src/pobsync_backend/tests/test_views.py

@@ -895,6 +895,50 @@ class ViewTests(TestCase):
         self.assertContains(response, ""ok": true")
         self.assertContains(response, reverse("snapshot_detail", args=[snapshot.id]))
 
+    def test_run_detail_links_existing_rsync_log(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+        with TemporaryDirectory() as tmp:
+            log_path = Path(tmp) / "snapshot" / "meta" / "rsync.log"
+            log_path.parent.mkdir(parents=True)
+            log_path.write_text("rsync log line\n", encoding="utf-8")
+            run = BackupRun.objects.create(
+                host=host,
+                status=BackupRun.Status.SUCCESS,
+                snapshot_path=str(log_path.parent.parent),
+                result={"ok": True, "log": str(log_path)},
+            )
+
+            response = self.client.get(reverse("run_detail", args=[run.id]))
+            log_response = self.client.get(reverse("run_rsync_log", args=[run.id]))
+            log_body = b"".join(log_response.streaming_content)
+
+        self.assertContains(response, reverse("run_rsync_log", args=[run.id]))
+        self.assertContains(response, str(log_path))
+        self.assertEqual(log_response.status_code, 200)
+        self.assertEqual(log_body, b"rsync log line\n")
+
+    def test_run_detail_infers_rsync_log_from_snapshot_path(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+        with TemporaryDirectory() as tmp:
+            snapshot_path = Path(tmp) / "snapshot"
+            log_path = snapshot_path / "meta" / "rsync.log"
+            log_path.parent.mkdir(parents=True)
+            log_path.write_text("scheduled log\n", encoding="utf-8")
+            run = BackupRun.objects.create(
+                host=host,
+                status=BackupRun.Status.SUCCESS,
+                snapshot_path=str(snapshot_path),
+                result={"ok": True},
+            )
+
+            response = self.client.get(reverse("run_rsync_log", args=[run.id]))
+            body = b"".join(response.streaming_content)
+
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(body, b"scheduled log\n")
+
     def test_run_detail_offers_cancel_for_running_run(self) -> None:
         self.client.force_login(self.staff_user)
         host = HostConfig.objects.create(host="web-01", address="web-01.example.test")