fix(feishu): lazy-load lark sdk during gateway startup

tests/channels/test_feishu_lazy_import.py

@@ -0,0 +1,46 @@
+import subprocess
+import sys
+
+
+def _run_import_probe(source: str) -> str:
+    proc = subprocess.run(
+        [sys.executable, "-c", source],
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+    return proc.stdout.strip()
+
+
+def test_feishu_module_import_does_not_import_lark_oapi():
+    out = _run_import_probe(
+        "import sys; import nanobot.channels.feishu; print('lark_oapi' in sys.modules)"
+    )
+
+    assert out == "False"
+
+
+def test_feishu_channel_constructor_does_not_import_lark_oapi():
+    out = _run_import_probe(
+        "import sys; "
+        "from nanobot.bus.queue import MessageBus; "
+        "from nanobot.channels.feishu import FeishuChannel; "
+        "FeishuChannel({'enabled': True}, MessageBus()); "
+        "print('lark_oapi' in sys.modules)"
+    )
+
+    assert out == "False"
+
+
+def test_lark_runtime_thread_import_clears_sdk_import_loop():
+    out = _run_import_probe(
+        "import asyncio\n"
+        "from nanobot.channels.feishu import _load_lark_runtime\n"
+        "async def main():\n"
+        "    await asyncio.to_thread(_load_lark_runtime)\n"
+        "    import lark_oapi.ws.client as ws\n"
+        "    print(getattr(ws, 'loop', 'sentinel') is None)\n"
+        "asyncio.run(main())"
+    )
+
+    assert out == "True"