feat: dynamically set PORT from Dockerfile, add .env.example

.env.example

@@ -0,0 +1,14 @@
+# optional, used for fetching build logs, not configured automatically
+RAILWAY_TOKEN=your_railway_token_here
+
+# optional but automatically configured by Railway
+# RAILWAY_PROJECT_ID=your_project_id_here
+# RAILWAY_SERVICE_ID=your_service_id_here
+# RAILWAY_ENVIRONMENT_ID=your_environment_id_here
+# RAILWAY_DEPLOYMENT_ID=your_deployment_id_here
+
+# optional, automatically configured by Railway
+# PORT=5800
+
+# optional, has a default you may not want
+# RAILWAY_PUBLIC_DOMAIN=your-domain.railway.app