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

crates/aether-contracts/Cargo.toml

@@ -7,7 +7,8 @@ repository.workspace = true
 description = "Shared contracts for Python and Rust Aether components"
 
 [dependencies]
+bytes.workspace = true
+flate2.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 thiserror.workspace = true
-