fix(ui): home page order and visibility bugs

- home_pages_mask XOR toggle initialises to HP_ALL before flipping bit,
  preventing accidental hiding of all other pages when mask starts at 0
- buildVisibleOrder appends any visible page missing from custom page_order,
  so pages absent from migrated/corrupted prefs remain navigable

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

examples/companion_radio/ui-new/SettingsScreen.h

@@ -600,6 +600,7 @@ public:
         return true;
       }
       if (enter && homePageToggleable(_selected)) {
+        if (!p->home_pages_mask) p->home_pages_mask = HP_ALL;
         p->home_pages_mask ^= homePageBit(_selected);
         _dirty = true;
         return true;