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

src/chat/mcpclient.h

@@ -0,0 +1,93 @@
+// SPDX-FileCopyrightText: 2026 GXDE OS Team
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <QHash>
+#include <QJsonArray>
+#include <QJsonObject>
+#include <QObject>
+#include <QStringList>
+
+#include <functional>
+
+class QProcess;
+
+/**
+ * One MCP server speaking JSON-RPC 2.0 over stdio.
+ */
+class McpServer : public QObject
+{
+    Q_OBJECT
+
+public:
+    McpServer(const QString &name, const QString &command, const QStringList &args,
+              QObject *parent = nullptr);
+    ~McpServer() override;
+
+    void start();
+
+    QString name() const { return m_name; }
+    bool ready() const { return m_ready; }
+    QJsonArray tools() const { return m_tools; }
+
+    void callTool(const QString &tool, const QJsonObject &arguments,
+                  std::function<void(const QJsonObject &)> callback);
+
+signals:
+    void readyChanged();
+
+private:
+    void send(const QJsonObject &message);
+    void handleLine(const QByteArray &line);
+    void finishToolList();
+
+    QString m_name;
+    QString m_command;
+    QStringList m_args;
+    QProcess *m_process = nullptr;
+    QByteArray m_buffer;
+    int m_nextId = 1;
+    QHash<int, std::function<void(const QJsonObject &)>> m_callbacks;
+    QJsonArray m_tools;
+    bool m_ready = false;
+};
+
+/**
+ * Aggregates the configured MCP servers and exposes their tools in the
+ * OpenAI function-calling format.
+ */
+class McpManager : public QObject
+{
+    Q_OBJECT
+
+public:
+    static McpManager *instance();
+
+    void reload();
+
+    bool hasTools() const;
+    QJsonArray toolDefinitions() const;
+    QStringList statusLines() const;
+
+    void callTool(const QString &exposedName, const QJsonObject &arguments,
+                  std::function<void(const QJsonObject &)> callback);
+
+signals:
+    void toolsChanged();
+
+private:
+    explicit McpManager(QObject *parent = nullptr);
+    void clearServers();
+    void rebuild();
+
+    QList<McpServer *> m_servers;
+    struct ToolRoute
+    {
+        McpServer *server = nullptr;
+        QString originalName;
+    };
+    QHash<QString, ToolRoute> m_routes;
+    QJsonArray m_definitions;
+    QStringList m_status;
+};