feat(docker): add Docker deployment configuration

Add production-ready Docker setup with multi-stage Dockerfile, docker-compose
orchestration for API, PostgreSQL, Redis, and Nginx services. Includes
health checks, non-root user execution, and proper networking.

- Add multi-stage Dockerfile with gunicorn/gevent workers
- Add docker-compose.yml with api, db, redis, nginx services
- Add nginx reverse proxy configuration with security headers
- Update .env.example with Docker and production variables
- Add email provider configuration (Mailgun, SendGrid)
- Add requests dependency for HTTP client support
- Update documentation with Docker deployment guide
- Rebrand project name from Gatehouse to Secuird

.gitignore

@@ -136,6 +136,7 @@ Thumbs.db
 # Project specific
 
 *.db
+flask_session/
 
 # Opencode files and folders
 .opencode/