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/providers/proxmox.py

@@ -0,0 +1,56 @@
+from typing import Any
+
+import httpx
+
+from app.services.providers.base import Provider, ProviderConnection
+
+
+class ProxmoxProvider(Provider):
+    name = "proxmox"
+
+    async def test_connection(self, connection: ProviderConnection) -> dict[str, Any]:
+        async with httpx.AsyncClient(verify=connection.verify_tls, timeout=10) as client:
+            response = await client.get(
+                f"{connection.api_url.rstrip('/')}/api2/json/version",
+                headers={"Authorization": connection.token},
+            )
+            response.raise_for_status()
+            return response.json().get("data", {})
+
+    async def sync_inventory(self, connection: ProviderConnection) -> dict[str, list[dict[str, Any]]]:
+        async with httpx.AsyncClient(verify=connection.verify_tls, timeout=20) as client:
+            resources = await client.get(
+                f"{connection.api_url.rstrip('/')}/api2/json/cluster/resources",
+                headers={"Authorization": connection.token},
+            )
+            resources.raise_for_status()
+            data = resources.json().get("data", [])
+
+        nodes = [item for item in data if item.get("type") == "node"]
+        workloads = [item for item in data if item.get("type") in {"qemu", "lxc"}]
+        networks = await self.list_networks(connection)
+        return {"nodes": nodes, "workloads": workloads, "networks": networks}
+
+    async def list_networks(self, connection: ProviderConnection) -> list[dict[str, Any]]:
+        async with httpx.AsyncClient(verify=connection.verify_tls, timeout=20) as client:
+            resources = await client.get(
+                f"{connection.api_url.rstrip('/')}/api2/json/cluster/resources",
+                headers={"Authorization": connection.token},
+            )
+            resources.raise_for_status()
+            data = resources.json().get("data", [])
+        return [item for item in data if item.get("type") in {"network", "sdn"}]
+
+    async def preview_rules(self, connection: ProviderConnection, rules: list[dict[str, Any]]) -> dict[str, Any]:
+        return {
+            "provider": self.name,
+            "read_only": connection.read_only,
+            "generated": rules,
+            "warnings": ["Preview only. No Proxmox firewall changes were sent."],
+        }
+
+    async def apply_rules(self, connection: ProviderConnection, rules: list[dict[str, Any]]) -> dict[str, Any]:
+        if connection.read_only:
+            return {"applied": False, "reason": "Cluster is read-only", "rules": rules}
+        return {"applied": False, "reason": "Apply adapter intentionally requires explicit implementation", "rules": rules}
+