The setup wizard's provider/model pickers (curses_radiolist via
prompt_choice) bailed to the numbered "Select [1-N]" fallback the moment
a user pressed up or down. Root cause: even with keypad(True) — which
curses.wrapper sets — many terminals/terminfo entries deliver cursor keys
to getch() as raw CSI/SS3 byte sequences (e.g. 27, 91, 66 for arrow-down)
rather than the translated curses.KEY_DOWN. The menus matched only
curses.KEY_UP/KEY_DOWN and treated the leading 27 (ESC) as cancel, so
navigation dropped into the text fallback and the trailing bytes leaked
into the next input().
Add a shared read_menu_key() helper that decodes CSI/SS3 escape sequences
into normalized NAV_* actions (only a lone ESC, with no continuation byte
within a short timeout, still cancels) and consumes the tail of unhandled
sequences so stray bytes can't corrupt later input(). Route all three
curses menus (checklist, radiolist, single_select) through it.
Add regression tests covering raw CSI/SS3 arrows, translated KEY_*
constants, vim keys, lone-ESC cancel, and full consumption of unhandled
sequences (Delete/Home/End).
