fix(qq-fm): guard FM start when offline + reset radar page on re-login [#88 review]

- startFm() now refuses with 'Bot is not connected to TeamSpeak' before mutating the
  queue, so POST /api/player/:id/fm can no longer wipe the queue and flip the bot into
  FM mode while disconnected (the !fm chat command already had this guard).
- The /fm route's success detection also treats 'not connected' as a failure so the
  toast type is correct.
- QQMusicProvider.setCookie() resets radarPage to 1 so a re-login with a different
  account no longer inherits the previous account's radar pagination cursor.

src/music/qq.ts

@@ -462,6 +462,9 @@ export class QQMusicProvider implements MusicProvider {
 
   setCookie(cookie: string): void {
     this.cookie = cookie;
+    // Reset radar pagination so a re-login (different account) starts from the
+    // first page rather than inheriting the previous account's cursor.
+    this.radarPage = 1;
   }
 
   getCookie(): string {