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/web/src/api/client.js

@@ -91,6 +91,7 @@ export const api = {
     dm: {
         list: () => request('GET', '/dm'),
         create: (data) => request('POST', '/dm', data),
+        close: (id) => request('DELETE', `/dm/${id}`),
         messages: (id, before, limit = 50) => {
             const params = new URLSearchParams();
             if (before)

packages/web/src/api/client.ts

@@ -149,6 +149,7 @@ export const api = {
   dm: {
     list: () => request<DmChannel[]>('GET', '/dm'),
     create: (data: CreateDmRequest) => request<DmChannel>('POST', '/dm', data),
+    close: (id: string) => request<{ success: boolean }>('DELETE', `/dm/${id}`),
     messages: (id: string, before?: string, limit = 50) => {
       const params = new URLSearchParams();
       if (before) params.set('before', before);