feat: DM infrastructure overhaul + volume sliders + LiveKit dynamic URL

- Add DM edit/delete endpoints (REST + WebSocket)
- Add DM typing indicators with real-time broadcast
- Fix volume sliders to control LiveKit mic/speaker
- Fix Send Message button on user profile popout
- Add New DM modal with user search
- Fix message pagination (SQL cursor instead of in-memory)
- Guard optional attachments on DM messages
- Dynamic LiveKit URL from request Host header
- DM sidebar auto-sorts by most recent message

packages/web/src/api/client.js

@@ -99,6 +99,8 @@ export const api = {
             return request('GET', `/dm/${id}/messages?${params}`);
         },
         sendMessage: (id, data) => request('POST', `/dm/${id}/messages`, data),
+        updateMessage: (id, data) => request('PATCH', `/dm/messages/${id}`, data),
+        deleteMessage: (id) => request('DELETE', `/dm/messages/${id}`),
     },
     social: {
         friends: () => request('GET', '/social/friends'),