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/Message.hpp

@@ -0,0 +1,55 @@
+// 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 <QString>
+
+#include "session/ContentBlock.hpp"
+
+namespace QodeAssist::Session {
+
+enum class MessageRole { User, Assistant, System };
+
+struct Usage
+{
+    int promptTokens = 0;
+    int completionTokens = 0;
+    int cachedPromptTokens = 0;
+    int reasoningTokens = 0;
+
+    bool isEmpty() const
+    {
+        return promptTokens == 0 && completionTokens == 0 && cachedPromptTokens == 0
+               && reasoningTokens == 0;
+    }
+
+    bool operator==(const Usage &other) const = default;
+
+    friend QDebug operator<<(QDebug debug, const Usage &usage)
+    {
+        return debug.nospace() << "Usage(" << usage.promptTokens << ", " << usage.completionTokens
+                               << ", " << usage.cachedPromptTokens << ", " << usage.reasoningTokens
+                               << ")";
+    }
+};
+
+struct Message
+{
+    MessageRole role = MessageRole::User;
+    QString id;
+    QList<ContentBlock> blocks;
+    Usage usage;
+
+    bool operator==(const Message &other) const = default;
+
+    friend QDebug operator<<(QDebug debug, const Message &message)
+    {
+        return debug.nospace() << "Message(role=" << int(message.role) << ", id=" << message.id
+                               << ", blocks=" << message.blocks << ", " << message.usage << ")";
+    }
+};
+
+} // namespace QodeAssist::Session