feat: add Docker deployment (backend:18889, frontend:18888)

- Dockerfile.backend: Python 3.11 + FastAPI + uvicorn
- Dockerfile.frontend: Node 20 build + Nginx serve
- docker-compose.yml: orchestration with data volume mount
- nginx.conf: API/WebSocket proxy to backend
- web/backend/requirements.txt: Python dependencies
- .dockerignore: exclude venv/node_modules/data from build

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Dockerfile.frontend

@@ -0,0 +1,18 @@
+# Build stage
+FROM node:20-alpine AS build
+
+WORKDIR /app
+COPY web/frontend/package.json web/frontend/package-lock.json* ./
+RUN npm install
+COPY web/frontend/ .
+RUN npm run build
+
+# Production stage
+FROM nginx:alpine
+
+COPY --from=build /app/dist /usr/share/nginx/html
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+
+EXPOSE 18888
+
+CMD ["nginx", "-g", "daemon off;"]