Round of hardenings on the experimental Tui component:

• Bound input buffers (paste, pending control sequences, undo, FIGlet ZIP); paste overflow now surfaces a visible marker rather than a silent drop. Paste cap aligned to 16 MiB to match FileInputHelper.
• Strip control bytes in LoaderWidget messages and UTF-8 C1 in VirtualTerminal::setTitle() to close OSC-injection vectors.
• Fix BracketedPasteTrait to preserve bytes that preceded the paste start marker instead of folding them into the paste buffer.
• FocusManager::clear() now also clears the focused widget reference; TickEvent is always dispatched so listeners can hint busy state without an onTick callback.
• LoaderWidget no longer auto-starts in the constructor; call start() explicitly.
• ProgressBarWidget::tick() advances the bar offset in indeterminate mode.
• Document the raw-passthrough contract on TextWidget, SelectListWidget, SettingItem, and InputWidget::setPrompt().