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/auth/mod.rs

@@ -0,0 +1,10 @@
+mod runtime;
+mod trusted;
+
+pub(crate) use runtime::{
+    resolve_execution_runtime_auth_context, should_buffer_request_for_local_auth,
+    GatewayControlAuthContext,
+};
+pub(crate) use trusted::{
+    request_model_local_rejection, trusted_auth_local_rejection, GatewayLocalAuthRejection,
+};

apps/aether-gateway/src/auth/runtime.rs

@@ -0,0 +1,4 @@
+pub(crate) use super::super::control::{
+    resolve_execution_runtime_auth_context, should_buffer_request_for_local_auth,
+    GatewayControlAuthContext,
+};

apps/aether-gateway/src/auth/trusted.rs

@@ -0,0 +1,3 @@
+pub(crate) use super::super::control::{
+    request_model_local_rejection, trusted_auth_local_rejection, GatewayLocalAuthRejection,
+};