fix(media): publish status when a track ends naturally

The Redis media:status key was only rewritten after a command received via
Redis. When the last track ended naturally (AudioPlayer Idle -> advanceQueue
with an empty queue), currentTrackItem was cleared but the status key was not
persisted — so the backend's cached status and the frontend's 10s polling
stayed stuck showing the finished track as 'playing' forever.

Wire a media-status sink (commandHandler provides the real redisPub to
MediaHandler) and re-publish status after auto-advance, so natural track end
updates the UI.

services/discord-gateway/src/modules/command-handler/mediaStatusSink.ts

@@ -0,0 +1,41 @@
+import type Redis from "ioredis";
+import { createChildLogger } from "@/shared/logger/index";
+import { MEDIA_STATUS_KEY } from "../../shared/redis-channels.js";
+
+/**
+ * Shared sink for writing the media status Redis key.
+ *
+ * CommandHandler owns the publisher + status writes for command-triggered
+ * changes (`publishMediaStatus`). MediaHandler needs to also persist status
+ * when the queue advances *outside* a command (natural track end / screen-share
+ * done), so we expose the real publisher here and let CommandHandler wire it
+ * once at startup.
+ */
+const logger = createChildLogger("media-status-sink");
+
+let _setMediaStatusKey: ((payload: unknown) => void) | null = null;
+
+export function setMediaStatusWriter(writer: (payload: unknown) => void): void {
+  _setMediaStatusKey = writer;
+}
+
+export function setMediaStatusKey(payload: unknown): void {
+  if (!_setMediaStatusKey) {
+    logger.warn("Media status writer not wired — skipping status publish");
+    return;
+  }
+  _setMediaStatusKey(payload);
+}
+
+export { MEDIA_STATUS_KEY };
+
+export function wireMediaStatusWriter(redisPub: Redis): void {
+  setMediaStatusWriter((payload) => {
+    redisPub
+      .set(MEDIA_STATUS_KEY, JSON.stringify(payload))
+      .catch((err: unknown) => {
+        const msg = err instanceof Error ? err.message : String(err);
+        logger.warn({ error: msg }, "Failed to update media status key");
+      });
+  });
+}