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

tests/mcptest.cpp

@@ -0,0 +1,60 @@
+// SPDX-FileCopyrightText: 2026 GXDE OS Team
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+// Headless MCP smoke test: starts the given command as an MCP server, waits for
+// tools/list and calls the first tool once.
+
+#include <QCoreApplication>
+#include <QJsonDocument>
+#include <QTextStream>
+#include <QTimer>
+
+#include "chat/mcpclient.h"
+
+int main(int argc, char *argv[])
+{
+    QCoreApplication app(argc, argv);
+    QTextStream out(stdout);
+
+    if (argc < 3) {
+        out << "usage: " << argv[0] << " <command> <script> [args...]\n";
+        return 2;
+    }
+
+    QStringList args;
+    for (int i = 2; i < argc; ++i) {
+        args.append(QString::fromLocal8Bit(argv[i]));
+    }
+
+    McpServer server(QStringLiteral("test"), QString::fromLocal8Bit(argv[1]), args);
+
+    QObject::connect(&server, &McpServer::readyChanged, [&]() {
+        out << "READY tools=" << server.tools().size() << "\n";
+        if (server.tools().isEmpty()) {
+            app.exit(1);
+            return;
+        }
+        const QString name =
+            server.tools().first().toObject().value(QStringLiteral("name")).toString();
+        out << "TOOL " << name << "\n";
+        server.callTool(name, QJsonObject{ { QStringLiteral("text"),
+                                             QStringLiteral("hello") } },
+                        [&](const QJsonObject &result) {
+                            out << "RESULT "
+                                << QString::fromUtf8(
+                                       QJsonDocument(result).toJson(QJsonDocument::Compact))
+                                << "\n";
+                            out.flush();
+                            app.quit();
+                        });
+    });
+
+    server.start();
+    QTimer::singleShot(8000, &app, [&]() {
+        out << "TIMEOUT\n";
+        out.flush();
+        app.exit(1);
+    });
+
+    return app.exec();
+}