defaultCopyAction function
Reads the engine's selection text and writes it to the system clipboard.
Used as the default Copy action so a TerminalView with no host wiring
still performs the natural Ctrl+Shift+C.
Implementation
void defaultCopyAction(TerminalEngine engine) {
final text = engine.selectionText();
if (text != null && text.isNotEmpty) {
Clipboard.setData(ClipboardData(text: text));
}
}