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/app/core/deps.py

@@ -0,0 +1,25 @@
+from fastapi import Depends, Header, HTTPException, Request, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.config import Settings, get_settings
+from app.core.database import get_session
+
+
+async def get_db(session: AsyncSession = Depends(get_session)) -> AsyncSession:
+    return session
+
+
+def get_app_settings() -> Settings:
+    return get_settings()
+
+
+async def require_admin(
+    request: Request,
+    authorization: str | None = Header(default=None),
+    settings: Settings = Depends(get_app_settings),
+) -> None:
+    token = None
+    if authorization and authorization.lower().startswith("bearer "):
+        token = authorization.split(" ", 1)[1]
+    if token != settings.admin_token:
+        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid admin token")