feat(chat): MCP stdio 工具接入

- McpServer：启动进程、initialize、tools/list、tools/call
- McpManager：多服务器、工具名冲突处理、OpenAI function 定义
- ChatClient：请求携带 tools，流式累积 tool_calls，结束后交回上层
- ChatWindow：工具调用循环（最多 5 轮）、scaffold 消息、设置里的 MCP JSON 编辑
- 无头自测 gxde-ai-see-mcptest + tests/mcp/test_server.py 验证通过

CMakeLists.txt

@@ -34,6 +34,7 @@ set(GXDE_AI_SEE_SOURCES
     src/todo/todowindow.cpp
     src/chat/chatclient.cpp
     src/chat/chatwindow.cpp
+    src/chat/mcpclient.cpp
     src/ui/portalpanel.cpp
 )
 
@@ -73,6 +74,14 @@ add_executable(gxde-ai-see-selftest
 target_include_directories(gxde-ai-see-selftest PRIVATE src ${ICU_INCLUDE_DIRS})
 target_link_libraries(gxde-ai-see-selftest PRIVATE Qt6::Core Qt6::Gui ${ICU_LIBRARIES})
 
+add_executable(gxde-ai-see-mcptest
+    tests/mcptest.cpp
+    src/chat/mcpclient.cpp
+    src/config.cpp
+)
+target_include_directories(gxde-ai-see-mcptest PRIVATE src)
+target_link_libraries(gxde-ai-see-mcptest PRIVATE Qt6::Core)
+
 install(TARGETS gxde-ai-see RUNTIME DESTINATION bin)
 install(FILES data/gxde-ai-see.desktop data/gxde-ai-see-todo.desktop DESTINATION share/applications)
 install(DIRECTORY data/icons/ DESTINATION share/icons/hicolor)