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/Dockerfile

@@ -0,0 +1,22 @@
+FROM python:3.12-slim AS runtime
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1 \
+    PIP_NO_CACHE_DIR=1
+
+WORKDIR /app
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends build-essential curl \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY pyproject.toml ./
+RUN pip install --upgrade pip \
+    && pip install ".[test]"
+
+COPY app ./app
+COPY tests ./tests
+
+EXPOSE 8000
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 CMD curl -fsS http://localhost:8000/health || exit 1
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]