fix(ui): clearok(stdscr) in ui_resume to clear vim screen residue

ncurses didn't know the editor clobbered the physical screen, so the
first refresh after vim exit was a no-op diff. Stale frame stayed
visible until the next keystroke triggered readline redisplay.

src/ui/core.c

@@ -198,6 +198,7 @@ void
 ui_resume(void)
 {
     ui_suspended = FALSE;
+    clearok(stdscr, TRUE); // ncurses can't see vim's screen clobber
     refresh();
     inp_resume();
 }