fix: resolve silent voice playback on VPS and queue screenshare streams

- Call unpause() when starting a stream in DiscordPlayer to prevent getting stuck in a paused state.
- Call stop() instead of pause() in VoiceController on disconnect to fully reset the player.
- Add user-agent header to ffmpeg calls in MusicPlayer and Transcoder to prevent YouTube 403 Forbidden on VPS.
- Add screenshare streams to the media queue when successfully started.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/voiceController.ts

@@ -159,7 +159,7 @@ export class VoiceController {
       stopRecording(this.activeGuildId);
     }
 
-    discordPlayer.pause();
+    discordPlayer.stop();
     this.activeGuildId = null;
     this.activeChannelId = null;
     this.activeChannelName = null;