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/base.py

@@ -0,0 +1,50 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import Any
+
+
+@dataclass(frozen=True)
+class ProviderConnection:
+    api_url: str
+    token: str
+    verify_tls: bool = True
+    read_only: bool = True
+
+
+class HypervisorProvider(ABC):
+    @abstractmethod
+    async def test_connection(self, connection: ProviderConnection) -> dict[str, Any]:
+        raise NotImplementedError
+
+
+class InventoryProvider(ABC):
+    @abstractmethod
+    async def sync_inventory(self, connection: ProviderConnection) -> dict[str, list[dict[str, Any]]]:
+        raise NotImplementedError
+
+
+class NetworkProvider(ABC):
+    @abstractmethod
+    async def list_networks(self, connection: ProviderConnection) -> list[dict[str, Any]]:
+        raise NotImplementedError
+
+
+class FirewallProvider(ABC):
+    @abstractmethod
+    async def preview_rules(self, connection: ProviderConnection, rules: list[dict[str, Any]]) -> dict[str, Any]:
+        raise NotImplementedError
+
+    @abstractmethod
+    async def apply_rules(self, connection: ProviderConnection, rules: list[dict[str, Any]]) -> dict[str, Any]:
+        raise NotImplementedError
+
+
+class Provider(
+    HypervisorProvider,
+    InventoryProvider,
+    NetworkProvider,
+    FirewallProvider,
+    ABC,
+):
+    name: str
+