feat(bleed): add working Quit to _show_menus via runner_params.app_shall_exit

Adds 'manual slop' menu before 'Windows' in the live HelloImGui menubar callback.
Quit sets self.runner_params.app_shall_exit = True — the correct HelloImGui API.
Previously the only quit path was the window close button.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gui_2.py

@@ -1613,6 +1613,10 @@ class App:
     # ---------------------------------------------------------------- gui
 
  def _show_menus(self) -> None:
+  if imgui.begin_menu("manual slop"):
+   if imgui.menu_item("Quit", "Ctrl+Q", False)[0]:
+    self.runner_params.app_shall_exit = True
+   imgui.end_menu()
   if imgui.begin_menu("Windows"):
    for w in self.show_windows.keys():
     _, self.show_windows[w] = imgui.menu_item(w, "", self.show_windows[w])