chore: initial project setup with backend, frontend, CI/CD, and documentation

Add complete NexaFabric project structure including:
- FastAPI backend with SQLAlchemy models, JWT auth, RBAC, audit logging, and provider interfaces
- React + TypeScript frontend with Vite, Tailwind CSS, TanStack Query, and Zustand
- Docker Compose configuration for PostgreSQL, Redis, API, worker, frontend, and nginx
- GitHub Actions and GitLab CI workflows for testing, linting, building, and security scanning
- Environment

deploy/systemd/nexafabric-agent.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=NexaFabric Node Agent
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+EnvironmentFile=-/etc/nexafabric/agent.env
+ExecStart=/usr/local/bin/nexafabric-agent
+Restart=on-failure
+RestartSec=5
+User=root
+
+[Install]
+WantedBy=multi-user.target
+