fix: use dedicated internal port to avoid collision with PORT env

If a platform injects PORT=3000 (e.g. Railway), nginx and Next.js
would both try to bind port 3000. Use a dedicated internal port (7901)
for the nginx→Next.js proxy to prevent this.

nginx.conf

@@ -7,7 +7,6 @@ http {
         listen ${PORT};
         listen [::]:${PORT};
 
-        # Route websockets traffic to port 3001
         location /websockets {
             proxy_pass http://${HOSTNAME}:3001;
             proxy_http_version 1.1;
@@ -16,9 +15,8 @@ http {
             proxy_set_header Host $http_host;
         }
 
-        # Route all other traffic to port 3000
         location / {
-            proxy_pass http://${HOSTNAME}:3000;
+            proxy_pass http://${HOSTNAME}:${INTERNAL_NEXTJS_PORT};
             proxy_set_header Host $http_host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

scripts/run.sh

@@ -18,13 +18,10 @@ fi
 export AUTH_SECRET=$(openssl rand -base64 32)
 
 export PORT=${PORT:-7575}
+export INTERNAL_NEXTJS_PORT=7901
 
-# Start nginx proxy
-# 1. Replace the HOSTNAME and PORT in the nginx template file
-# 2. Create the nginx configuration file from the template
-# 3. Start the nginx server
 export HOSTNAME
-envsubst '${HOSTNAME} ${PORT}' < /etc/nginx/templates/nginx.conf > /etc/nginx/nginx.conf
+envsubst '${HOSTNAME} ${PORT} ${INTERNAL_NEXTJS_PORT}' < /etc/nginx/templates/nginx.conf > /etc/nginx/nginx.conf
 # Start services in the background and store their PIDs
 nginx -g 'daemon off;' &
 NGINX_PID=$!
@@ -38,7 +35,7 @@ else
     REDIS_PID=$!
 fi
 
-PORT=3000 node apps/nextjs/server.js &
+PORT=$INTERNAL_NEXTJS_PORT node apps/nextjs/server.js &
 NEXTJS_PID=$!
 
 # Function to handle SIGTERM and shut down services