Add Ping frontend

React 19 + TypeScript client built with Vite. Zustand for local state,
react-oidc-context for the login flow, a SignalR connection for chat and
presence events, and LiveKit's React components for voice/video calls.

frontend/nginx.conf

@@ -0,0 +1,10 @@
+server {
+    listen 3100;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # SPA fallback: client-side routing (react-router) owns everything under /.
+    location / {
+        try_files $uri /index.html;
+    }
+}