feat(webui): Display logged-in username

- Add username display in the `SiteHeader` component.
- Update logout button text to include username.
- Add `username` field in auth state.
- Optimize token parsing logic to extract username information.
- pre-commit fix

env.example

@@ -155,4 +155,4 @@ REDIS_URI=redis://localhost:6379
 # AUTH_ACCOUNTS='admin:admin123,user1:pass456'     # username:password,username:password
 # TOKEN_SECRET=Your-Key-For-LightRAG-API-Server    # JWT key
 # TOKEN_EXPIRE_HOURS=4                             # expire duration
-# WHITELIST_PATHS=                                 # white list
+# WHITELIST_PATHS=                                 # white list