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

docs/upgrade.md

@@ -0,0 +1,10 @@
+# Upgrade Guide
+
+1. Read release notes.
+2. Back up PostgreSQL and secrets.
+3. Pull the new version.
+4. Run database migrations.
+5. Restart API, workers, frontend, and proxy.
+6. Run health checks.
+7. Generate a firewall preview before any apply workflow.
+