Add database foundation for observability features:
- event_log table with severity/source filtering and pagination
- standalone_proxies table for user-created reverse proxies
- stale_threshold_days setting (default 7 days)
- Auto-persist warn/error events from event bus to database
- SSE broadcast of persistent events for real-time UI updates
- Frontend types and API functions for downstream UI phases
Embed SvelteKit static build in Go binary via go:embed. Event bus
for pub/sub with deploy log, instance status, and deploy status events.
SSE endpoints for real-time streaming. Frontend SSE client with
exponential backoff reconnection. Makefile for build pipeline.
Update Phase 12 auth plan with OAuth2/OIDC support.