fix: Hub 连接清理顺序修复、OAuth 类型常量提取、disassociate 逻辑优化

- Hub proxy/worker 连接关闭时先 unregister 再延迟 abort writer，确保缓冲消息排空
- 提取 OAUTH_AUTH_TYPES 常量，替代各处硬编码的 OAuth 类型列表
- auto-disassociate 跳过 OAuth Key，避免其动态 allowed_models 干扰判定
- 删除 Key 时传入 skip_disassociate=True，跳过不必要的解关联检查
- ModelMapper 缓存命中时将 ORM 实例脱离 Session，修复 DetachedInstanceError

tests/services/test_provider_keys_key_command_service.py

@@ -202,7 +202,7 @@ def test_clear_oauth_invalid_response_invalidates_caches(
 
 
 @pytest.mark.asyncio
-async def test_run_delete_key_side_effects_not_skip_disassociate(
+async def test_run_delete_key_side_effects_skip_disassociate(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
     captured: dict[str, Any] = {}
@@ -225,4 +225,4 @@ async def test_run_delete_key_side_effects_not_skip_disassociate(
     )
 
     assert captured["provider_id"] == "provider-1"
-    assert "skip_disassociate" not in captured
+    assert captured["skip_disassociate"] is True