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

android/build.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    id("com.android.application") version "8.5.0" apply false
+    id("org.jetbrains.kotlin.android") version "1.9.24" apply false
+    id("com.google.gms.google-services") version "4.4.2" apply false
+}