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

tests/unit/test_tunnel_transport_factory.py

@@ -0,0 +1,14 @@
+from src.services.proxy_node.gateway_tunnel_transport import GatewayTunnelTransport
+from src.services.proxy_node.tunnel_protocol import Frame, MsgType
+from src.services.proxy_node.tunnel_transport import create_tunnel_transport
+
+
+def test_create_tunnel_transport_always_uses_gateway_tunnel_transport() -> None:
+    transport = create_tunnel_transport("node-1", timeout=12.0)
+    assert isinstance(transport, GatewayTunnelTransport)
+
+
+def test_tunnel_protocol_supports_node_status_msg_type() -> None:
+    raw = Frame(0, MsgType.NODE_STATUS, 0, b'{"node_id":"n1","connected":true}').encode()
+    decoded = Frame.decode(raw)
+    assert decoded.msg_type == MsgType.NODE_STATUS