refactor: Decoupling chat architecture (#367)

* refactor: Migrate tests to Qt Creator plugin framework and update llmqore transports

* refactor: Move conversation history into IDE-free session library

* refactor: Extract turn context assembly behind injected ports

* build: Add RunQodeAssistTests target for the plugin test suite

* refactor: Route the chat through a Session and ChatBackend seam

sources/session/ConversationHistory.hpp

@@ -0,0 +1,39 @@
+// Copyright (C) 2026 Petr Mironychev
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Additional attribution terms under GPLv3 §7(b) apply — see LICENSE
+
+#pragma once
+
+#include <QList>
+
+#include <functional>
+
+#include "session/Message.hpp"
+
+namespace QodeAssist::Session {
+
+class ConversationHistory
+{
+public:
+    void append(const Message &message);
+
+    qsizetype size() const;
+    const QList<Message> &messages() const;
+    const Message &at(qsizetype index) const;
+    const Message &last() const;
+    Message *lastMessage();
+
+    void visitBlocks(const std::function<void(ContentBlock &)> &visit);
+
+    bool operator==(const ConversationHistory &other) const = default;
+
+    friend QDebug operator<<(QDebug debug, const ConversationHistory &history)
+    {
+        return debug.nospace() << "History(" << history.m_messages << ")";
+    }
+
+private:
+    QList<Message> m_messages;
+};
+
+} // namespace QodeAssist::Session