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/troubleshooting.md

@@ -0,0 +1,19 @@
+# Troubleshooting
+
+## API Cannot Reach Proxmox
+
+- Verify Proxmox URL and TLS settings.
+- Check token format and least-privilege role assignment.
+- Test routing from the API container.
+
+## Login Fails
+
+- Confirm demo seed data was created.
+- Verify database connectivity.
+- Reset the local admin password through a controlled maintenance task.
+
+## Firewall Preview Is Empty
+
+- Confirm at least one enabled policy exists.
+- Check policy definition source, destination, service, action, and direction.
+