fix(lyric): 修复桌面歌词窗口首次打开无歌词问题

歌词窗口 Vue 加载完成后发送 lyric-ready 信号，主窗口收到后
发送完整歌词数据，替代不可靠的延迟猜测方案

src/preload/index.d.ts

@@ -19,6 +19,7 @@ interface API {
   sendSong: (data: any) => void;
   unblockMusic: (id: number, data: any, enabledSources?: string[]) => Promise<any>;
   onLyricWindowClosed: (callback: () => void) => void;
+  onLyricWindowReady: (callback: () => void) => void;
   getAppUpdateState: () => Promise<AppUpdateState>;
   checkAppUpdate: (manual?: boolean) => Promise<AppUpdateState>;
   downloadAppUpdate: () => Promise<AppUpdateState>;