refactor: 移除独立 hub/proxy/executor/gateway crate，统一为 gateway tunnel 架构

- 删除 aether-hub、aether-proxy 独立项目及其 Dockerfile/配置
- 删除 crates/aether-executor 和 crates/aether-gateway 全部模块
- 新增 apps/ 目录作为应用入口
- 将 hub 概念重构为 gateway tunnel transport
- 将 executor 重构为 execution runtime
- 新增 tunnel.rs 合约定义和 testkit tunnel/execution_runtime 模块
- 更新 Python 服务层和测试适配新架构命名

apps/aether-gateway/src/control/auth/mod.rs

@@ -0,0 +1,15 @@
+mod credentials;
+mod gate;
+mod principal;
+mod resolution;
+mod types;
+
+pub(crate) use credentials::extract_requested_model;
+pub(crate) use gate::{
+    request_model_local_rejection, should_buffer_request_for_local_auth,
+    trusted_auth_local_rejection, GatewayLocalAuthRejection,
+};
+pub(super) use resolution::{resolve_control_decision_auth, ControlDecisionAuthResolution};
+pub(crate) use resolution::{
+    resolve_execution_runtime_auth_context, GatewayAdminPrincipalContext, GatewayControlAuthContext,
+};