Add production hardening: health check, streamer panic fix, db maintenance

- Add health check endpoint at /.well-known/healthcheck.json that
  verifies database and RIS Live connectivity, returns 200/503

- Fix panic in streamer when encountering unknown RIS message types
  by logging a warning and continuing instead of crashing

- Add DBMaintainer for periodic database maintenance:
  - VACUUM every 6 hours to reclaim space
  - ANALYZE every hour to update query statistics
  - Graceful shutdown support

- Add Vacuum() and Analyze() methods to database interface

internal/database/interface.go

@@ -81,6 +81,10 @@ type Store interface {
 
 	// Lifecycle
 	Close() error
+
+	// Maintenance operations
+	Vacuum(ctx context.Context) error
+	Analyze(ctx context.Context) error
 }
 
 // Ensure Database implements Store