Add Codex auth preservation setting

src/types.ts

@@ -333,6 +333,8 @@ export interface Settings {
   streamCheckConfirmed?: boolean;
   // Whether to show the failover toggle independently on the main page
   enableFailoverToggle?: boolean;
+  // Preserve Codex ChatGPT login in auth.json when switching third-party providers
+  preserveCodexOfficialAuthOnSwitch?: boolean;
   // User has confirmed the failover toggle first-run notice
   failoverConfirmed?: boolean;
   // User has confirmed the first-run welcome notice