The RPi5 projector reports a 4K preferred mode although it is really 1080p;
previously only wlr_output_preferred_mode() was tried. --screen-mode picks
an exact resolution (highest refresh among matches, or an exact @Hz when a
refresh is given) from the output's mode list and, if the request cannot be
satisfied, prints every reported mode and exits before launching anything.
main(): consumes '--screen-mode <val>' and '--screen-mode=<val>' while
compacting the app list so the flag never becomes a tab launcher; malformed
values exit rc 2 with a usage hint. handle_new_output(): resolution/@Hz
match with list-and-exit fallback. On the headless backend the request
sizes the output, which also makes the flag testable.
tests: screen_mode_sets_output_size (dump PPM == 480x320), not consumed as
an app (both tabs boot, no 'starts with -' warning), bad values exit rc 2.
Andrew Hamilton
6ccb3e8d12