showContentTo method
Renders content only (no frame borders) to a provided RenderOutput.
Useful for embedding content within other frames or custom layouts.
Implementation
void showContentTo(
RenderOutput out, void Function(FrameContext ctx) content) {
final frame = FramedLayout(title, theme: theme);
final lb = LineBuilder(theme);
final ctx = FrameContext._(out, lb, theme, frame);
content(ctx);
}