Critical fixes:
- Fix StaleContainer frontend type to match nested backend response shape
- Guard ContainerID[:12] slice against empty/short IDs in ListAllProxies
High-priority fixes:
- Support comma-separated severity/source in event log filtering (IN clause)
- Eliminate N+1 queries in ListAllProxies and FindStaleInstances (pre-load maps)
- Stop leaking internal error messages to API clients (use slog + generic msgs)
alexei.dolgolyov
e0a648fb0c