[BDisp]

Fixes

• Fixes MenuItem.Key with BindKeyToApplication does not fire Action while PopoverMenu is closed #5757

Summary

• Allow application-scoped HotKey (KeyBinding.Target) in DefaultHotKeyHandler
  even when the view is not visible (closed PopoverMenu).
• Re-register BindKeyToApplication shortcuts once App is available
  (Shortcut.OnSuperViewChanged, MenuBarItem.EndInit).
• Unit test: MenuItem_BindKeyToApplication_Fires_Action_When_Popover_Closed.

Docs (follow-up or same PR)

• Clarify BindKeyToApplication in shortcut.md / menus.md MenuItem samples.
• Update command.md DefaultHotKeyHandler steps for visibility + app scope.

Test plan

• MenuItem_BindKeyToApplication_Fires_Action_When_Popover_Closed
• Existing KeyDown_App_Scope_* / MenuItem_HotKey_Fires_Action_When_Open

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[tig]

lgtm