Build frontend from source in Docker instead of pre-built static

Use multi-stage build:
- Stage 1: Node.js 20 builds frontend from source
- Stage 2: Python serves built static files

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -1,6 +1,24 @@
 # Dockerfile for HF Spaces (Docker SDK)
-# Uses pre-built frontend from static/ directory
+# Multi-stage build: Node.js for frontend, Python for backend
 
+# Stage 1: Build frontend
+FROM node:20-slim AS frontend-builder
+
+WORKDIR /frontend
+
+# Copy package files first for better caching
+COPY frontend/package.json frontend/package-lock.json ./
+
+# Install dependencies
+RUN npm ci
+
+# Copy frontend source code
+COPY frontend/ ./
+
+# Build the frontend
+RUN npm run build
+
+# Stage 2: Python backend with built frontend
 FROM python:3.11-slim
 
 WORKDIR /app
@@ -14,10 +32,9 @@ COPY src/ ./src/
 COPY a2a/ ./a2a/
 COPY data/ ./data/
 # Note: Don't copy .env file - HF Spaces injects secrets as environment variables
-# .env.example is for local development only
 
-# Copy pre-built frontend (built locally and committed)
-COPY static/ ./static/
+# Copy built frontend from stage 1
+COPY --from=frontend-builder /frontend/dist ./static/
 
 # Verify static files exist
 RUN ls -la /app/static/ && ls -la /app/static/assets/
@@ -29,5 +46,5 @@ EXPOSE 7860
 ENV PYTHONUNBUFFERED=1
 ENV PYTHONPATH=/app
 
-# Start server (using new consolidated path)
+# Start server
 CMD ["uvicorn", "src.api.app:app", "--host", "0.0.0.0", "--port", "7860"]