feat: support cross-origin WebSocket proxy for remote gateway

- Add nginx /gwproxy/ reverse proxy with correct Origin header
- Auto-detect cross-origin gateway URL in GatewayClient.connect()
- Detect path-based proxy deployment in LoginScreen getInitialUrl()
- Change nginx/Docker to listen on port 3000, use host network mode

docker-compose.yml

@@ -1,13 +1,11 @@
 services:
   pinchchat:
-    image: ghcr.io/marlburrow/pinchchat:latest
-    # Or build locally:
-    # build: .
-    ports:
-      - "3000:80"
+    # image: ghcr.io/marlburrow/pinchchat:latest
+    build: .
+    network_mode: host
     restart: unless-stopped
     healthcheck:
-      test: ["CMD", "wget", "-qO", "/dev/null", "http://localhost:80/"]
+      test: ["CMD", "wget", "-qO", "/dev/null", "http://localhost:3000/"]
       interval: 30s
       timeout: 3s
       start_period: 5s