feat(hub,stability): bounded outbound queue、worker liveness 检测、事件循环 watchdog 及 DB 操作异步化

- aether-hub: unbounded channel 改为 bounded channel (BoundedOutbound)，队列满时标记拥塞并主动关闭连接，防止内存无限增长
- aether-hub: worker idle timeout 从命令行参数改为基于心跳的 liveness 检测，默认 60 秒
- aether-hub: 新增 ConnConfig 统一管理连接配置，新增 outbound_queue_capacity 参数
- hub_transport: 新增事件循环 watchdog，检测 lag 超过阈值时临时降级暂停新流
- gunicorn_conf: 启用 faulthandler，worker abort 时自动 dump 全部线程栈用于诊断
- health/endpoint_checker/recording: 同步 DB 操作移至 asyncio.to_thread，避免阻塞事件循环
- Dockerfile: 移除 --worker-idle-timeout 0 命令行参数，改由环境变量和默认值控制

tests/unit/test_hub_transport_watchdog.py

@@ -0,0 +1,66 @@
+from __future__ import annotations
+
+import time
+
+import pytest
+
+from src.services.proxy_node.hub_config import HubConfig
+from src.services.proxy_node.hub_transport import HubConnectionManager
+from src.services.proxy_node.tunnel_manager import TunnelStreamError
+
+
+def _build_manager() -> HubConnectionManager:
+    return HubConnectionManager(
+        HubConfig(
+            enabled=True,
+            url="ws://127.0.0.1:8085",
+            connect_timeout_seconds=1.0,
+            ping_interval_seconds=1.0,
+            send_timeout_seconds=1.0,
+            max_streams=16,
+            max_frame_size=1024 * 1024,
+        )
+    )
+
+
+def test_record_loop_lag_warning_does_not_degrade() -> None:
+    manager = _build_manager()
+
+    manager._record_loop_lag(1.5)
+
+    assert manager._degraded_until == 0.0
+
+
+def test_record_loop_lag_degrades_manager(monkeypatch: pytest.MonkeyPatch) -> None:
+    manager = _build_manager()
+    now = 1234.0
+    monkeypatch.setattr("src.services.proxy_node.hub_transport._time.monotonic", lambda: now)
+
+    manager._record_loop_lag(4.0)
+
+    assert manager._degraded_until == pytest.approx(now + 12.0)
+
+
+@pytest.mark.asyncio
+async def test_send_request_rejects_while_manager_degraded(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    manager = _build_manager()
+    manager._degraded_until = time.monotonic() + 5.0
+
+    async def _fake_ensure_connected() -> None:
+        return None
+
+    monkeypatch.setattr(manager, "ensure_connected", _fake_ensure_connected)
+
+    with pytest.raises(TunnelStreamError, match="event loop degraded"):
+        await manager.send_request(
+            "node-1",
+            method="POST",
+            url="https://example.com/v1/chat/completions",
+            headers={"content-type": "application/json"},
+            body=b"{}",
+            timeout=5.0,
+        )
+
+    assert manager._pending_streams == {}