chore: remove Qwen support from SDK and internal components

- Deleted `QwenAuthenticator`, internal `qwen_auth`, and `qwen_executor` implementations.
- Removed all Qwen-related OAuth flows, token handling, and execution logic.
- Cleaned up dependencies and references to Qwen across the codebase.

sdk/cliproxy/service.go

@@ -107,7 +107,6 @@ func newDefaultAuthManager() *sdkAuth.Manager {
 		sdkAuth.NewGeminiAuthenticator(),
 		sdkAuth.NewCodexAuthenticator(),
 		sdkAuth.NewClaudeAuthenticator(),
-		sdkAuth.NewQwenAuthenticator(),
 	)
 }
 
@@ -423,8 +422,6 @@ func (s *Service) ensureExecutorsForAuthWithMode(a *coreauth.Auth, forceReplace
 		s.coreManager.RegisterExecutor(executor.NewAntigravityExecutor(s.cfg))
 	case "claude":
 		s.coreManager.RegisterExecutor(executor.NewClaudeExecutor(s.cfg))
-	case "qwen":
-		s.coreManager.RegisterExecutor(executor.NewQwenExecutor(s.cfg))
 	case "iflow":
 		s.coreManager.RegisterExecutor(executor.NewIFlowExecutor(s.cfg))
 	case "kimi":
@@ -903,9 +900,6 @@ func (s *Service) registerModelsForAuth(a *coreauth.Auth) {
 			}
 		}
 		models = applyExcludedModels(models, excluded)
-	case "qwen":
-		models = registry.GetQwenModels()
-		models = applyExcludedModels(models, excluded)
 	case "iflow":
 		models = registry.GetIFlowModels()
 		models = applyExcludedModels(models, excluded)