check -p and exec accept a navigation profile or menu whose home page or menu-item page/microflow does not exist #1569

Repro (v0.26.0, v0.27.0, current main, and #1564; Mendix 11.12.5)

create or replace navigation Responsive
  home page Shop.NoSuchHome
  menu (
    menu 'G' (
      menu item 'Bogus' page Shop.NoSuchPage;
      menu item 'Bogus2' microflow Shop.ACT_NoSuchFlow;
    );
    menu item 'Bogus3' page Shop.NoSuchPage3;
  );

The mdl 1 form behaves the same way:

create or modify navigation Responsive home page Shop.NoSuchHome {
  menu item 'Bogus' ( OnClick: show page Shop.NoSuchPage )
  menu 'G' { menu item 'Bogus2' ( OnClick: call microflow Shop.ACT_NoSuchFlow ) }
};

1. mxcli check nav.mdl -p app.mpr reports "Check passed!", with only deprecation warnings for the old form.
2. exec prints "Navigation profile 'Responsive' updated." and stores every item.
3. mx check is the first to object, with 4 × CE1613: "The selected page 'Shop.NoSuchHome' no longer exists." at the Navigation profile, and the same for each menu item's page or microflow.

show page and call microflow actions on a page are refused when their target doesn't exist, and so is an unknown icon. Navigation targets weren't among the reference kinds added for #1472. That includes the home page, which the original report didn't mention.

Why it matters

create or replace navigation replaces the menu it states (and, since #1522, keeps any clause it omits), and it is usually the last script of an apply. A renamed page or a typo in a menu target therefore passes per-file checks and lands in the model, and it only surfaces at the consistency check after everything has been applied. A run without mx check leaves a project that won't build.

Proposal

check -p reports an unresolved navigation or menu target, and exec refuses before writing, using the same resolution and wording as the existing page and flow reference checks. Targets created earlier in the same script, and targets in System or Marketplace modules, still resolve. I have a PR ready and will link it.