Change: Hide client chat dialog on close instead of terminating

Closing the client-side chat dialog (via the "end chat" button or the title-bar
X) now only hides the window and keeps the session alive, instead of destroying
it. Closing the chat stays server-initiated: the next message from the server
reopens the hidden dialog via the existing SW_RESTORE path in OnReceive, and the
dialog is only truly destroyed on COMMAND_CHAT_CLOSE or connection close.

Co-Authored-By: deepseek-v4-pro

client/ChatManager.cpp

@@ -245,14 +245,17 @@ INT_PTR CALLBACK CChatManager::ChatDialogProc(HWND hDlg, UINT uMsg, WPARAM wPara
             return TRUE;
         }
         if (LOWORD(wParam) == IDC_BUTTON_END) {
-            // 被控端主动结束交谈：关闭本地聊天窗口
-            SendMessage(hDlg, WM_USER + 1, NULL, NULL);
+            // 被控端关闭聊天窗口：仅隐藏对话框，会话保持。关闭交谈始终由服务端发起，
+            // 服务端继续发消息时 OnReceive 会用 SW_RESTORE 重新弹出本对话框。
+            ShowWindow(hDlg, SW_HIDE);
             return TRUE;
         }
         break;
 
     case WM_CLOSE:
-        return 0;
+        // X 关闭按钮：仅隐藏对话框（与「结束交谈」一致），关闭交谈始终由服务端发起
+        ShowWindow(hDlg, SW_HIDE);
+        return TRUE;
 
     case WM_USER + 1:
         pThis->m_hWnd = NULL;