e90d7dba76
After the operator pressed `y` on the preflight modal (or picked an agent in the picker), the modal's curses sub-window stayed on screen until the dashboard's main loop ticked again — which during a 5-10s launch made it look like the confirmation never registered. Add `_erase_modal` (touchwin + refresh on stdscr) and call it at every exit from `_preflight_modal` and `_picker_modal`. The pre-modal frame buffered on stdscr immediately overwrites the sub-window's area; the launch proceeds with a clean dashboard underneath.