An Apple TV's alert is answered by its remote, whichever way was asked (CHALLENGES 313)

[lana-20]

On an Apple TV, a dialog of three or more buttons was refused naming `app_alert` with `button` as the remedy. `button` presses by tapping, and a TV refuses every tap, so the remedy led to a second refusal. A two-button dialog was already right: accept and dismiss were refused naming the D-pad (CHALLENGES 298).

The fix: `app_alert` asks the driver (`mobiumdriver.AlertAnsweredByRemote`) before it chooses between accept, dismiss and a button. On a TV, all three are refused with the same D-pad instructions, and the dialog's buttons go in the details. `app_alert`'s schema and `mobium alert --help` no longer say `button` works "on any dialog".

Checked:

• On the Apple TV simulator (tvOS 26.5), `tv-app.sh` passed. It now asserts `--button` is refused naming the remote.
• `dialogs.sh` passed unchanged on the iPhone 17 Pro simulator.
• MobiumTV has no dialog of three buttons. The check runs before the buttons are counted, so its two-button dialog takes the same line.
• New unit test: `TestAppleTVAlertIsAnsweredByRemote`. `make ci` passes.