fix(editor): prevent UI redraw conflicts during editor suspend/resume

Guard against re-entrant editor launches, abort editor on Ctrl-Z,
and centralize suspend-aware redraws through prof_doupdate() to prevent
terminal corruption when SIGTSTP is received while editor is active.

Removes SIGUSR1 editor escape in favor of standard pkill <editor> recovery.

tests/unittests/ui/stub_ui.c

@@ -85,6 +85,10 @@ void
 ui_resize(void)
 {
 }
+void
+prof_doupdate(void)
+{
+}
 
 void
 ui_focus_win(ProfWin* win)
@@ -1475,3 +1479,13 @@ ui_is_suspended(void)
 {
     return FALSE;
 }
+
+void
+ui_beep(void)
+{
+}
+
+void
+ui_flash(void)
+{
+}