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/policy_engine.py

@@ -0,0 +1,35 @@
+from typing import Any
+
+from app.models.domain import Policy
+
+
+class PolicyEngine:
+    def compile(self, policy: Policy) -> dict[str, Any]:
+        definition = policy.definition or {}
+        source = definition.get("source", "any")
+        destination = definition.get("destination", "any")
+        service = definition.get("service", {"protocol": "any", "ports": "any"})
+        action = definition.get("action", "allow")
+        direction = definition.get("direction", "ingress")
+
+        generated_rule = {
+            "policy_id": policy.id,
+            "policy_version": policy.version,
+            "source": source,
+            "destination": destination,
+            "protocol": service.get("protocol", "any"),
+            "ports": service.get("ports", "any"),
+            "direction": direction,
+            "action": action,
+            "logging": bool(definition.get("logging", False)),
+            "description": definition.get("description", policy.name),
+        }
+
+        warnings = []
+        if source == "any" and destination == "any":
+            warnings.append("Policy targets all sources and destinations.")
+        if action == "allow" and service.get("ports") == "any":
+            warnings.append("Broad allow policy uses all ports.")
+
+        return {"rules": [generated_rule], "warnings": warnings, "conflicts": []}
+