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/bot/instance.ts

@@ -747,6 +747,12 @@ export class BotInstance extends EventEmitter {
   }
 
   async startFm(provider: MusicProvider = this.neteaseProvider): Promise<string> {
+    // Match the !fm chat-command guard: refuse before mutating the queue when
+    // offline, so the web /fm route can't wipe the queue + flip into FM mode
+    // while nothing can actually play.
+    if (!this.connected) {
+      return "Bot is not connected to TeamSpeak";
+    }
     if (!provider.getPersonalFm) {
       return `Personal FM is not available for ${provider.platform}`;
     }