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>

.dockerignore

@@ -0,0 +1,20 @@
+.venv/
+__pycache__/
+*.pyc
+.git/
+.gitignore
+.claude/
+.playwright-mcp/
+.trae/
+node_modules/
+web/frontend/node_modules/
+data/
+docs/
+tests/
+*.md
+!README.md
+release/
+dist/
+build/
+*.spec
+*.exe