Move npm build to Docker image build time (#4636)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile.ui

@@ -1,5 +1,8 @@
 FROM node:20.12-slim
 
+# Install tini for proper signal handling and zombie reaping
+RUN apt-get update && apt-get install -y --no-install-recommends tini && rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 COPY ./skyvern-frontend /app
 COPY ./entrypoint-skyvernui.sh /app/entrypoint-skyvernui.sh
@@ -8,6 +11,13 @@ RUN npm install
 ENV VITE_API_BASE_URL=http://localhost:8000/api/v1
 ENV VITE_WSS_BASE_URL=ws://localhost:8000/api/v1
 ENV VITE_ARTIFACT_API_BASE_URL=http://localhost:9090
+# Placeholder for runtime injection
+ENV VITE_SKYVERN_API_KEY=__SKYVERN_API_KEY_PLACEHOLDER__
 
-CMD [ "/bin/bash", "/app/entrypoint-skyvernui.sh" ]
+# Build at image time
+RUN npm run build
+
+# Use tini as init for proper signal handling and zombie reaping
+ENTRYPOINT ["/usr/bin/tini", "--"]
+CMD ["/bin/bash", "/app/entrypoint-skyvernui.sh"]