Harden frontend Docker npm fetch resilience

.env.example

@@ -41,6 +41,14 @@ PUBLIC_BASE_URL=http://localhost:8000
 CORS_ORIGINS=["http://localhost:5173","http://localhost:3000"]
 VITE_API_BASE=
 
+# Optional frontend build network and npm fetch tuning:
+DOCKER_BUILD_NETWORK=default
+NPM_REGISTRY=https://registry.npmjs.org/
+NPM_FETCH_RETRIES=5
+NPM_FETCH_RETRY_MINTIMEOUT=20000
+NPM_FETCH_RETRY_MAXTIMEOUT=120000
+NPM_FETCH_TIMEOUT=300000
+
 # Production baseline overrides (set explicitly for live deployments):
 # APP_ENV=production
 # HOST_BIND_IP=127.0.0.1