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/main.py

@@ -0,0 +1,42 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.api.v1.router import api_router
+from app.core.config import get_settings
+from app.db.session import Base, SessionLocal, engine
+from app.seed.demo import seed_demo_data
+
+
+def create_app() -> FastAPI:
+    settings = get_settings()
+    app = FastAPI(
+        title=settings.project_name,
+        description="SDN-like network and security control plane for Proxmox VE.",
+        version="0.1.0",
+        docs_url="/api/docs",
+        openapi_url="/api/openapi.json",
+    )
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=[str(origin) for origin in settings.cors_origins],
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+
+    @app.on_event("startup")
+    def startup() -> None:
+        Base.metadata.create_all(bind=engine)
+        with SessionLocal() as db:
+            seed_demo_data(db)
+
+    @app.get("/healthz")
+    def healthz() -> dict[str, str]:
+        return {"status": "ok"}
+
+    app.include_router(api_router, prefix="/api/v1")
+    return app
+
+
+app = create_app()
+