feat(docker): add frontend Dockerfile with nginx configuration
- Created multi-stage Dockerfile for frontend build and deployment
- Builder stage: npm ci, TypeScript compilation, Vite build
- Production stage: nginx Alpine serving static assets
- Added nginx.conf with SPA routing, gzip compression, security headers
- Created frontend/.dockerignore to optimize build context
- Added health check endpoint at /health for container orchestration
- Documented build strategy, optimization, and deployment in docs/docker-frontend.md
- Verified: npm build succeeds (Docker build pending availability)
1504986d0b