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>

web/backend/requirements.txt

@@ -0,0 +1,19 @@
+# Web backend dependencies
+fastapi>=0.104.0
+uvicorn[standard]>=0.24.0
+python-jose[cryptography]>=3.3.0
+bcrypt>=4.0.0
+python-multipart>=0.0.6
+httpx>=0.25.0
+werkzeug>=3.0.0
+
+# Core app dependencies (needed by processing endpoints)
+pandas>=1.3.0
+openpyxl>=3.0.0
+xlrd>=2.0.0,<2.1.0
+xlwt>=1.3.0
+xlutils>=2.0.0
+numpy>=1.19.0
+requests>=2.25.0
+python-dotenv>=1.0.0
+configparser>=5.0.0