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.cpp

@@ -0,0 +1,47 @@
+// Copyright (C) 2026 Petr Mironychev
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Additional attribution terms under GPLv3 §7(b) apply — see LICENSE
+
+#include "session/ConversationHistory.hpp"
+
+namespace QodeAssist::Session {
+
+void ConversationHistory::append(const Message &message)
+{
+    m_messages.append(message);
+}
+
+qsizetype ConversationHistory::size() const
+{
+    return m_messages.size();
+}
+
+const QList<Message> &ConversationHistory::messages() const
+{
+    return m_messages;
+}
+
+const Message &ConversationHistory::at(qsizetype index) const
+{
+    return m_messages.at(index);
+}
+
+const Message &ConversationHistory::last() const
+{
+    return m_messages.last();
+}
+
+Message *ConversationHistory::lastMessage()
+{
+    return m_messages.isEmpty() ? nullptr : &m_messages.last();
+}
+
+void ConversationHistory::visitBlocks(const std::function<void(ContentBlock &)> &visit)
+{
+    for (Message &message : m_messages) {
+        for (ContentBlock &block : message.blocks)
+            visit(block);
+    }
+}
+
+} // namespace QodeAssist::Session