--no-alt-screen was silently removed with no replacement — alt-screen is now unavoidable and broken

Alt-screen/fullscreen mode is a genuine regression for a lot of us, and it's
been reported since March (#1799, #2334) with no resolution.

What makes this worse: the --no-alt-screen flag that used to let people
opt out has now been removed entirely, with no deprecation notice and no
replacement setting. Running it now just fails:

$ copilot --no-alt-screen
error: unknown option '--no-alt-screen'

I checked /settings for an equivalent key and found nothing that restores
inline/streaming rendering. So as of the current release, there is no
supported way to turn off fullscreen mode at all.

This isn't a nice-to-have. Alt-screen breaks:

• native terminal scrollback (can't scroll up past the current screen)
• terminal search (Cmd+F / Ctrl+F can't see history)
• copy/paste in some terminal emulators
• usability in tmux/screen and browser-based terminals

Please either:

1. Restore --no-alt-screen (or an equivalent /settings key), or
2. Clearly document the replacement if one exists and I'm missing it.

Removing an escape hatch that people were actively relying on, without
warning, is a bad pattern. At minimum this needs a documented workaround.

Commencez par reproduire copilot --no-alt-screen et inspectez /settings pour voir les contrôles actuels de alt-screen. Suivez l’option CLI et les points d’entrée de Settings afin de déterminer si un équivalent existe ou si le flag doit être rétabli. Le travail est terminé lorsque le rendu inline ou en streaming peut être désactivé via une interface prise en charge et documentée, sans générer l’échec d’option inconnue.