feat: real-time sync, notification & social system overhaul

- Add WS events: dm_channel_created, dm_channel_closed, friend_removed,
  channel_created/updated/deleted, server_updated
- Fix first-ever DM: broadcast dm_channel_created to recipient
- Add DELETE /api/dm/:id for closing DMs with re-open support
- Wire Close DM button in sidebar
- Fix dm_message_created for unknown channels (safety net)
- Broadcast friend_removed on friend deletion
- Sound system: track realtimeMessageEvents separately from API loads,
  play notification for messages in all channels, not just current
- Optimistic updates: send/edit/delete messages appear instantly with
  rollback on failure, temp message deduplication on WS echo
- Channel CRUD broadcasts to all server members
- Server update broadcast on PATCH
- Server join registers user in connectionManager immediately
- Reconnect: only reload current channel, preserve other channel caches
- Activity panel, right panel, member list toggle components

packages/shared/src/types.ts

@@ -213,6 +213,13 @@ export type ServerEvent =
   | { type: 'dm_call_rejected'; dmChannelId: string }
   | { type: 'dm_call_ended'; dmChannelId: string }
   | { type: 'voice_status_update'; userId: string; channelId: string; isMuted: boolean; isDeafened: boolean }
+  | { type: 'dm_channel_created'; dmChannel: DmChannel }
+  | { type: 'dm_channel_closed'; dmChannelId: string }
+  | { type: 'friend_removed'; userId: string }
+  | { type: 'channel_created'; channel: Channel; serverId: string }
+  | { type: 'channel_updated'; channel: Channel; serverId: string }
+  | { type: 'channel_deleted'; channelId: string; serverId: string }
+  | { type: 'server_updated'; server: Server }
   | { type: 'error'; message: string };
 
 // ─── API Request/Response Types ─────────────────────────────────────────────