feat(android): add device activation flow and update dependencies

重构项目架构，引入启动页(SplashActivity)检查激活状态，未激活设备引导至激活页(ActivationActivity)完成provision+token流程。集成Retrofit+RxJava3网络层、Room数据库、Lifecycle组件、MMKV等依赖，升级OkHttp/Gson版本，并将构建配置从旧项目全面迁移至新项目结构。

WebRTCSignalServer/src/main/java/com/ttstd/signaling/controller/AuthController.java

@@ -150,7 +150,6 @@ public class AuthController {
         body.put("displayName", principal.displayName());
         body.put("sessionId", principal.sessionId());
         body.put("signalDeviceId", principal.deviceId());
-        body.put("admin", principal.admin());
         // 便于客户端展示"是否已开启双因子"，仅对用户身份有效
         if (principal.isUser()) {
             body.put("totpEnabled",