fix: [Experimental hotfix 1] Fix Signaling issues Toju App

1. Server: WebSocket ping/pong heartbeat (index.ts)
Added a 30-second ping interval that pings all connected clients
Connections without a pong response for 45 seconds are terminated and cleaned up
Extracted removeDeadConnection() to deduplicate the cleanup logic between close events and dead connection reaping
2. Server: Fixed sendServerUsers filter bug (handler.ts:13)
Removed && cu.displayName from the filter — users who joined a server before their identify message was processed were silently invisible to everyone. This was the direct cause of "can't see each other" in session 2.
3. Client: Typing message now includes serverId
Added serverId: this.webrtc.currentServerId to the typing payload
Added a currentServerId getter on WebRTCService

server/src/websocket/handler.ts

@@ -10,7 +10,7 @@ interface WsMessage {
 /** Sends the current user list for a given server to a single connected user. */
 function sendServerUsers(user: ConnectedUser, serverId: string): void {
   const users = Array.from(connectedUsers.values())
-    .filter(cu => cu.serverIds.has(serverId) && cu.oderId !== user.oderId && cu.displayName)
+    .filter(cu => cu.serverIds.has(serverId) && cu.oderId !== user.oderId)
     .map(cu => ({ oderId: cu.oderId, displayName: cu.displayName ?? 'Anonymous' }));
 
   user.ws.send(JSON.stringify({ type: 'server_users', serverId, users }));