Fixed: #499 #985

feat(oauth): add support for customizable OAuth callback ports

- Introduced `oauth-callback-port` flag to override default callback ports.
- Updated SDK and login flows for `iflow`, `gemini`, `antigravity`, `codex`, `claude`, and `openai` to respect configurable callback ports.
- Refactored internal OAuth servers to dynamically assign ports based on the provided options.
- Revised tests and documentation to reflect the new flag and behavior.

internal/cmd/anthropic_login.go

@@ -32,9 +32,10 @@ func DoClaudeLogin(cfg *config.Config, options *LoginOptions) {
 	manager := newAuthManager()
 
 	authOpts := &sdkAuth.LoginOptions{
-		NoBrowser: options.NoBrowser,
-		Metadata:  map[string]string{},
-		Prompt:    promptFn,
+		NoBrowser:    options.NoBrowser,
+		CallbackPort: options.CallbackPort,
+		Metadata:     map[string]string{},
+		Prompt:       promptFn,
 	}
 
 	_, savedPath, err := manager.Login(context.Background(), "claude", cfg, authOpts)