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

backend/app/services/firewall_orchestrator.py

@@ -0,0 +1,29 @@
+from app.models.domain import Cluster, Policy
+from app.schemas.domain import FirewallPreview
+from app.services.policy_engine import PolicyEngine
+from app.services.providers.base import ProviderConnection
+from app.services.providers.registry import get_provider
+
+
+class FirewallOrchestrator:
+    def __init__(self) -> None:
+        self.policy_engine = PolicyEngine()
+
+    async def preview(self, cluster: Cluster, policy: Policy) -> FirewallPreview:
+        compiled = self.policy_engine.compile(policy)
+        provider = get_provider(cluster.provider)
+        connection = ProviderConnection(
+            api_url=cluster.api_url,
+            token=cluster.token_ref or "",
+            verify_tls=cluster.verify_tls,
+            read_only=cluster.mode == "read_only",
+        )
+        provider_preview = await provider.preview_rules(connection, compiled["rules"])
+        return FirewallPreview(
+            policy_id=policy.id,
+            dry_run=True,
+            generated_rules=provider_preview["generated"],
+            warnings=[*compiled["warnings"], *provider_preview.get("warnings", [])],
+            conflicts=compiled["conflicts"],
+        )
+