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-proxy/docker-compose.yml

@@ -0,0 +1,14 @@
+services:
+  aether-proxy:
+    image: ghcr.io/fawney19/aether-proxy:latest
+    container_name: aether-proxy
+    restart: unless-stopped
+    env_file:
+      - .env
+    environment:
+      AETHER_PROXY_LOG_JSON: "true"
+    logging:
+      driver: json-file
+      options:
+        max-size: "50m"
+        max-file: "3"