feat: persist refreshed IDC tokens to auth file

Add persistRefreshedAuth function to write refreshed tokens back to the
auth file after inline token refresh. This prevents repeated token
refreshes on every request when the token expires.

Changes:
- Add persistRefreshedAuth() to kiro_executor.go
- Call persist after all token refresh paths (401, 403, pre-request)
- Remove unused log import from sdk/auth/kiro.go

internal/auth/kiro/sso_oidc.go

@@ -334,7 +334,7 @@ func (c *SSOOIDCClient) RefreshTokenWithRegion(ctx context.Context, clientID, cl
 	}
 
 	if resp.StatusCode != http.StatusOK {
-		log.Debugf("token refresh failed (status %d): %s", resp.StatusCode, string(respBody))
+		log.Warnf("IDC token refresh failed (status %d): %s", resp.StatusCode, string(respBody))
 		return nil, fmt.Errorf("token refresh failed (status %d)", resp.StatusCode)
 	}