chore: initial project setup with backend, frontend, Android app, and CI/CD

Add complete NexaMFA push MFA system with:
- FastAPI backend with PostgreSQL, Redis, OIDC provider, and Prometheus metrics
- React TypeScript admin console
- Android Kotlin/Jetpack Compose app with biometric authentication
- Docker Compose deployment configuration
- Gitea CI workflow for backend, frontend, and Android builds
- Environment configuration template with security settings
- Documentation for security model, deployment

backend/tests/test_api.py

@@ -0,0 +1,14 @@
+import os
+
+os.environ["DATABASE_URL"] = "sqlite+aiosqlite:///:memory:"
+os.environ["ENVIRONMENT"] = "test"
+
+from app.main import app
+from fastapi.testclient import TestClient
+
+
+def test_health_endpoint():
+    with TestClient(app) as client:
+        response = client.get("/health")
+        assert response.status_code == 200
+        assert response.json()["status"] == "ok"