Serve production frontend via Nginx static build

.env.example

@@ -39,7 +39,9 @@ PROVIDER_BASE_URL_ALLOWLIST=[]
 
 PUBLIC_BASE_URL=http://localhost:8000
 CORS_ORIGINS=["http://localhost:5173","http://localhost:3000"]
+# Used at build time for production frontend image, and at runtime in development.
 VITE_API_BASE=
+# Development-only Vite host allowlist override.
 VITE_ALLOWED_HOSTS=
 
 # Optional frontend build network and npm fetch tuning: