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

docker-compose.yml

@@ -0,0 +1,47 @@
+services:
+  postgres:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_DB: ${POSTGRES_DB:-nexamfa}
+      POSTGRES_USER: ${POSTGRES_USER:-nexamfa}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-nexamfa}
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-nexamfa} -d ${POSTGRES_DB:-nexamfa}"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  redis:
+    image: redis:7-alpine
+    command: ["redis-server", "--appendonly", "yes"]
+    volumes:
+      - redis_data:/data
+    healthcheck:
+      test: ["CMD", "redis-cli", "ping"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+  backend:
+    build: ./backend
+    env_file: .env
+    depends_on:
+      postgres:
+        condition: service_healthy
+      redis:
+        condition: service_healthy
+    ports:
+      - "8000:8000"
+
+  frontend:
+    build: ./frontend
+    depends_on:
+      - backend
+    ports:
+      - "8080:80"
+
+volumes:
+  postgres_data:
+  redis_data: