chore(per-instance-hook-scoping): archive verified+synced change

Move to openspec/changes/archive/2026-07-09-per-instance-hook-scoping/
(R100 renames preserved). 9 artifacts. Canonical openspec/specs/
service-instance-scoping/ remains. Resolves multi-instance wrong-data bug
(hooks now scope by instance.id; instance switcher re-scopes).
Carry-overs: fetchBackupDashboard untouched (design decision 5); subquery
scoping for runs/alerts (schema asymmetry).

backend/src/media_library_viewer_api/routers/backups.py

@@ -183,7 +183,10 @@ def get_backup_alerts(
     store: SettingsStore = Depends(get_settings_store),
 ) -> list[BackupAlertResponse]:
     alerts = store.list_backup_alerts(
-        job_id=job_id, acknowledged=acknowledged, severity=severity, service_id=service_id,
+        job_id=job_id,
+        acknowledged=acknowledged,
+        severity=severity,
+        service_id=service_id,
     )
     return [BackupAlertResponse(**alert) for alert in alerts]