fix(tui): make :cquit work properly with remote TUI (#25313)

src/nvim/main.c

@@ -659,6 +659,9 @@ void os_exit(int r)
 
   if (ui_client_channel_id) {
     ui_client_stop();
+    if (r == 0) {
+      r = ui_client_exit_status;
+    }
   } else {
     ui_flush();
     ui_call_stop();

src/nvim/tui/tui.c

@@ -386,6 +386,9 @@ static void terminfo_stop(TUIData *tui)
   unibi_out_ext(tui, tui->unibi_ext.disable_extended_keys);
   // May restore old title before exiting alternate screen.
   tui_set_title(tui, (String)STRING_INIT);
+  if (ui_client_exit_status == 0) {
+    ui_client_exit_status = tui->seen_error_exit;
+  }
   // if nvim exited with nonzero status, without indicated this was an
   // intentional exit (like `:1cquit`), it likely was an internal failure.
   // Don't clobber the stderr error message in this case.