feat(gateway): close video burst promptly when a user's SSRC is removed

ssrcMap emits "delete" when a VoiceUserData is removed (user stops sharing /
leaves voice). Hook it to close the user's open video burst ~500ms later so the
ffmpeg mux starts as soon as they stop, instead of waiting up to 5s for the idle
sweep. No-op if no burst exists; safe on normal teardown.

services/discord-gateway/src/modules/voice-recording/videoReceiver.ts

@@ -336,6 +336,14 @@ export function hookVideoReceiver(
 
   // If a user's video SSRC disappears, close their burst after a short grace so
   // the tail flushes.
+  receiver.ssrcMap.on("delete", (data) => {
+    // data = the deleted VoiceUserData (userId + audioSSRC). Close any open
+    // video burst for that user so the mux starts as soon as they stop sharing.
+    if (data?.userId) {
+      setTimeout(() => closeBurst(data.userId), 500);
+    }
+  });
+
   setInterval(() => {
     const now = Date.now();
     for (const [userId, burst] of bursts) {