feat: record backup snapshots during run completion

Upsert SnapshotRecord rows directly from run_pobsync_backup results so
new successful and failed backup runs are reflected in the database
without requiring a separate discovery pass. Keep discovery for existing
snapshots and repair workflows, and cover success, failure, and dry-run
behavior with tests.

src/pobsync_backend/management/commands/run_pobsync_backup.py

@@ -11,6 +11,7 @@ from pobsync.commands.run_scheduled import run_scheduled
 from pobsync.paths import PobsyncPaths
 from pobsync_backend.config_source import DjangoConfigSource
 from pobsync_backend.models import BackupRun, HostConfig
+from pobsync_backend.snapshot_discovery import infer_snapshot_kind, upsert_snapshot_record
 
 
 class Command(BaseCommand):
@@ -73,6 +74,13 @@ class Command(BaseCommand):
                 "result",
             ],
         )
+        if run.snapshot_path:
+            snapshot_path = Path(run.snapshot_path)
+            try:
+                kind = infer_snapshot_kind(snapshot_path)
+                upsert_snapshot_record(host=host, kind=kind, snapshot_dir=snapshot_path)
+            except ValueError:
+                pass
 
         if result.get("ok"):
             self.stdout.write(self.style.SUCCESS(f"Backup completed for {host.host}."))