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_gateway_tunnel_transport_stream_cleanup.py

@@ -0,0 +1,41 @@
+from __future__ import annotations
+
+import pytest
+
+from src.services.proxy_node.gateway_tunnel_transport import TunnelRelayResponseStream
+
+
+class _FakeResponse:
+    def __init__(self, chunks: list[bytes]) -> None:
+        self._chunks = chunks
+        self.closed = False
+
+    async def aiter_raw(self):  # type: ignore[override]
+        for chunk in self._chunks:
+            yield chunk
+
+    async def aclose(self) -> None:
+        self.closed = True
+
+
+@pytest.mark.asyncio
+async def test_tunnel_relay_response_stream_closes_after_iteration() -> None:
+    response = _FakeResponse([b"hello", b"world"])
+    stream = TunnelRelayResponseStream(response)  # type: ignore[arg-type]
+
+    chunks = []
+    async for chunk in stream:
+        chunks.append(chunk)
+
+    assert chunks == [b"hello", b"world"]
+    assert response.closed is True
+
+
+@pytest.mark.asyncio
+async def test_tunnel_relay_response_stream_aclose_closes_response() -> None:
+    response = _FakeResponse([])
+    stream = TunnelRelayResponseStream(response)  # type: ignore[arg-type]
+
+    await stream.aclose()
+
+    assert response.closed is True