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/stores/socialStore.ts

@@ -16,6 +16,8 @@ interface SocialState {
   searchUsers: (query: string) => Promise<User[]>;
   addIncomingRequest: (request: FriendRequest) => void;
   addFriendFromAccepted: (friend: Friend, requestId: string) => void;
+  updateFriendPresence: (userId: string, status: string) => void;
+  removeFriendLocally: (userId: string) => void;
 }
 
 export const useSocialStore = create<SocialState>((set, get) => ({
@@ -121,4 +123,20 @@ export const useSocialStore = create<SocialState>((set, get) => ({
       requests: state.requests.filter(r => r.id !== requestId),
     }));
   },
+
+  // Called from WS handler when the other user removes us as a friend
+  removeFriendLocally: (userId: string) => {
+    set((state) => ({
+      friends: state.friends.filter(f => f.id !== userId),
+    }));
+  },
+
+  // Called from WS handler on presence_update to keep friend status live
+  updateFriendPresence: (userId: string, status: string) => {
+    set((state) => ({
+      friends: state.friends.map(f =>
+        f.id === userId ? { ...f, status: status as Friend['status'] } : f
+      ),
+    }));
+  },
 }));