- Introduce Server.AttachWebsocketRoute(path, handler) to mount websocket
upgrade handlers on the Gin engine.
- Track registered WS paths via wsRoutes with wsRouteMu to prevent
duplicate registrations; initialize in NewServer and import sync.
- Add Manager.UnregisterExecutor(provider) for clean executor lifecycle
management.
- Add github.com/gorilla/websocket v1.5.3 dependency and update go.sum.
Motivation: enable services to expose WS endpoints through the core server
and allow removing auth executors dynamically while avoiding duplicate
route setup. No breaking changes.
