refactor(gemini-web): Remove auto-refresh, auto-close, and caching

This commit simplifies the Gemini web client by removing several complex, stateful features. The previous implementation for auto-refreshing cookies and auto-closing the client involved background goroutines, timers, and file system caching, which made the client's lifecycle difficult to manage.

The following features have been removed:
- The cookie auto-refresh mechanism, including the background goroutine (`rotateCookies`) and related configuration fields.
- The file-based caching for the `__Secure-1PSIDTS` token. The `rotate1PSIDTS` function now fetches a new token on every call.
- The auto-close functionality, which used timers to close the client after a period of inactivity.
- Associated configuration options and methods (`WithAccountLabel`, `WithOnCookiesRefreshed`, `Close`, etc.).

By removing this logic, the client becomes more stateless and predictable. The responsibility for managing the client's lifecycle and handling token expiration is now shifted to the caller, leading to a simpler and more robust integration.

sdk/cliproxy/service.go

@@ -322,9 +322,6 @@ func (s *Service) Run(ctx context.Context) error {
 	// Prefer core auth manager auto refresh if available.
 	if s.coreManager != nil {
 		interval := 15 * time.Minute
-		if sec := s.cfg.GeminiWeb.TokenRefreshSeconds; sec > 0 {
-			interval = time.Duration(sec) * time.Second
-		}
 		s.coreManager.StartAutoRefresh(context.Background(), interval)
 		log.Infof("core auth auto-refresh started (interval=%s)", interval)
 	}