feat(system): implement graceful shutdown and expand websocket events

Improve system reliability and real-time capabilities by implementing a robust lifecycle management system and adding new broadcast events for attachments and voice recordings.

- Implement asynchronous graceful shutdown in backend to close HTTP, WebSocket, Redis, and database connections.
- Add new WebSocket broadcast events: `attachment_created`, `voice_recording_started`, `voice_recording_stopped`, `voice_recording_uploaded`, and `analysis_queue_status`.
- Refactor media status handling to use boolean `playing` state instead of string-based status.
- Centralize `PageResult` and `VoiceRecording` types to improve consistency between frontend and backend.
- Update frontend API client to include `listRecordings` and handle new WebSocket event types.
- Fix type mismatches in voice command handling and media status reporting.

services/backend/src/modules/media/media.service.ts

@@ -47,8 +47,14 @@ export async function getStatus(): Promise<MediaState> {
   const cached = await readRedisStatus("media:status");
 
   if (cached) {
+    const rawPlaying = cached.playing;
+    // Handle both boolean (new) and string (legacy from String(discordPlayer.getStatus()))
+    const playing =
+      rawPlaying === true ||
+      rawPlaying === "playing" ||
+      rawPlaying === "buffering";
     return {
-      playing: Boolean(cached.playing),
+      playing,
       musicVolume: Number(cached.musicVolume ?? 1.0),
       current: (cached.current as MediaItem | null) ?? null,
       queue: (cached.queue as MediaItem[]) ?? [],