Replayable text-input validation and cancellation examples

[PerchAnton]

Would optional, portable text-input regression traces be useful here?

I built an external adapter calling textinput.Model Init/Update/View. Three scenarios cover Unicode edits, validation before submission, length limits, resize and Ctrl+C cancellation. All 15 steps, adapter race tests and go vet pass locally.

I maintain the experimental interaction-check runner. It remains separate test tooling, with no application runtime dependency. The adapter skips blink scheduling and does not use a real terminal. It exercises text input, so it does not duplicate the selection-scrolling fix in #39.