fix: QR login now persists cookies, shows server-generated QR image, passes timestamp

- Auth router accepts CookieStore and persists cookies on login
- NeteaseProvider passes timestamp to prevent cached QR responses
- QR image from server used directly (qrimg field)
- Cookie saved to disk on confirmed QR scan

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/music/provider.ts

@@ -43,6 +43,7 @@ export interface SearchResult {
 
 export interface QrCodeResult {
   qrUrl: string;
+  qrImg?: string; // base64 data URL of QR image
   key: string;
 }