FeaturesGrid, Tabs, Accordion, PricingTable, Testimonials, Gallery,
ContentSlider, NumberCounter, Menu, SocialLinks, Navbar and ContactForm
store their content in array props rather than Craft child nodes, so
the Layers tree showed nothing underneath them. This adds the pure
deriveVirtualRows() function and VIRTUAL_CHILD_PROPS registry the
Layers panel will consume in a later task.
Verified the registry against each component's actual item interface:
corrected Tabs (label field is `label`, not `title` -- TabItem has no
`title`) and Content Slider (label field is `heading`, not `title` --
Slide has no `title`). Both would have silently fallen back to
"Tab N" / "Slide N" for every existing site.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
