fix(deploy): build frontend in node stage

Dockerfile

@@ -1,14 +1,23 @@
+FROM node:20-slim AS frontend-build
+
+WORKDIR /frontend
+
+COPY frontend/package.json frontend/package-lock.json ./
+COPY frontend/tsconfig.json frontend/tsconfig.app.json frontend/tsconfig.node.json ./
+COPY frontend/vite.config.ts frontend/eslint.config.js frontend/index.html ./
+COPY frontend/public ./public
+COPY frontend/src ./src
+
+RUN npm ci && npm run build
+
+
 FROM python:3.11-slim
 
 WORKDIR /app
 
-# System deps + Node.js for frontend build
+# System deps
 RUN apt-get update && apt-get install -y --no-install-recommends \
         curl \
-        gnupg \
-    && curl -fsSL https://deb.nodesource.com/setup_20.x | bash - \
-    && apt-get install -y --no-install-recommends \
-        nodejs \
     && rm -rf /var/lib/apt/lists/*
 
 # Copy & install Python deps first for layer caching
@@ -18,8 +27,8 @@ RUN pip install --no-cache-dir -r requirements.txt
 # Copy application
 COPY . .
 
-# Build the copied React frontend so FastAPI can serve it at /
-RUN cd frontend && npm ci && npm run build
+# Copy the built frontend bundle from the Node stage so FastAPI can serve it at /
+COPY --from=frontend-build /frontend/dist ./frontend/dist
 
 # Install package so [project.scripts] is callable
 RUN pip install --no-cache-dir -e .