feat: persistent minibuffer output with *Messages* buffer

Implemented a persistent *Messages* buffer to capture all output from the minibuffer, ensuring that transient messages are logged and accessible. This addresses the issue of command output not always being visible to the user, providing a complete history for review.

include/lumacs/gtk_editor.hpp

@@ -46,6 +46,7 @@ private:
     Glib::RefPtr<Gtk::Application> app_;
     Gtk::Window* window_ = nullptr;
     Gtk::DrawingArea* drawing_area_ = nullptr; // Raw pointer to the main drawing area if single window
+    Gtk::DrawingArea* minibuffer_drawing_area_ = nullptr; // Dedicated drawing area for minibuffer
     Gtk::Widget* content_widget_ = nullptr; // The root widget of the editor content (Paned or DrawingArea)
     
     // For cursor blinking logic