fix(ui): add authoritative suspend flag gating redraws over the editor

Builds on the upstream "guard terminal writes while suspended" fix. That
fix keeps isendwin() a valid "suspended" signal by guarding stray writes
(_inp_write, beep, flash) so the existing isendwin() checks in
ui_update/ui_resize/ui_redraw hold. That is correct but fail-open: any
future unguarded doupdate()/refresh() reachable during an editor session
clears isendwin() and the ~10Hz ui_update() repaints over the editor
again (the original bug class).

Track suspension explicitly with a ui_suspended flag set in
ui_suspend()/ui_resume() and gate the three redraw entry points on
ui_suspended || isendwin() via _ui_redraw_suspended(). The flag is set
exactly at the suspend/resume boundary, so the dominant repaint path
fails safe regardless of isendwin() flapping. isendwin() is kept in the
condition for the shutdown/closed-screen case.

src/ui/inputwin.c

@@ -312,7 +312,7 @@ inp_get_line(void)
     wmove(inp_win, 0, 0);
     _inp_win_update_virtual();
     // Don't write to the terminal while suspended (external editor active).
-    if (!isendwin()) {
+    if (!is_suspended && !isendwin()) {
         doupdate();
     }
     char* line = NULL;
@@ -342,7 +342,7 @@ inp_get_password(void)
     wmove(inp_win, 0, 0);
     _inp_win_update_virtual();
     // Don't write to the terminal while suspended (external editor active).
-    if (!isendwin()) {
+    if (!is_suspended && !isendwin()) {
         doupdate();
     }
     char* password = NULL;