Add y/N re-auth confirmation to zai-auth command

src/cli/zai-auth.ts

@@ -27,6 +27,14 @@ async function promptHidden(question: string): Promise<string> {
   return answer.trim();
 }
 
+async function promptYesNo(question: string): Promise<boolean> {
+  const rl = readline.createInterface({ input: process.stdin, output: process.stdout, terminal: true });
+  const answer = await new Promise<string>((resolve) => rl.question(question, resolve));
+  rl.close();
+  const normalized = answer.trim().toLowerCase();
+  return normalized === 'y' || normalized === 'yes';
+}
+
 export function registerZaiAuthCommand(program: Command): void {
   program
     .command('zai-auth')
@@ -35,8 +43,11 @@ export function registerZaiAuthCommand(program: Command): void {
       const existing = loadStoredZaiAuth();
       if (existing) {
         console.log('Z.AI credential already exists.');
-        console.log('Delete ~/.config/flynn/auth.json zai/zhipuai entry if you want to re-authenticate.');
-        process.exit(0);
+        const confirmed = await promptYesNo('Re-authenticate and replace it? (y/N): ');
+        if (!confirmed) {
+          console.log('Cancelled.');
+          process.exit(0);
+        }
       }
 
       console.log('Z.AI uses API keys (HTTP Bearer), not an OAuth device flow.');