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>

tests/media/musicPlayer.test.ts

@@ -56,6 +56,8 @@ describe("createMusicPlayer", () => {
         "-hide_banner",
         "-loglevel",
         "warning",
+        "-user_agent",
+        "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36",
         "-i",
         "https://example.com/song.mp3",
         "-vn",