Add nginx reverse proxy and environment configuration

- Add nginx.conf for proxying API requests to backend
- Update frontend Dockerfile for production build with nginx
- Move hardcoded values to .env variables in docker-compose.yml
- Add .env.example template for configuration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/Dockerfile

@@ -1,18 +1,18 @@
-FROM node:20-slim
+# Build stage
+FROM node:20-slim AS build
 
 WORKDIR /app
 
-# Copy package files
-COPY package.json .
-
-# Install dependencies
+COPY package.json package-lock.json* ./
 RUN npm install
 
-# Copy source files
 COPY . .
+RUN npm run build
 
-# Expose port
-EXPOSE 5173
+# Production stage - just serve static files
+FROM nginx:alpine
 
-# Run dev server
-CMD ["npm", "run", "dev"]
+# Copy built frontend
+COPY --from=build /app/dist /usr/share/nginx/html
+
+EXPOSE 80