fix(vendor): embed batch (virtuallist, focus, zindex, text, classname styles)

[RuudBurger]

Promotes framework change(s) developed against the client's vendor/react-lightning embed.

What changed

• VirtualList back-stops the reveal gate so cells that never report a measure still show up
• useDerivedValue(() => withTiming(...)) ticks to a live number instead of storing the raw animation descriptor
• PixelRatio.get() reports 1, matching the fixed-resolution Lightning scene
• Focus events bubble up the element tree like tvOS/web, so wrapper views see child focus
• zIndex stacking is contained to the RN parent under view flattening instead of leaking scene-wide
• Grid focus resolves the target index with the cross axis, fixing down-navigation landing in the wrong column
• Colorless text defaults to white, and nested text aggregates re-fold correctly
• Vertical VirtualLists get a zero flex basis so content height can't inflate the ancestor flex chain
• VirtualList understands the native snap props (snapToAlignment/scrollSnapAlign, scrollSnapOffset, snapToItemPadding)
• className styles survive style-only updates, flexbox reset defaults to column again, and children append at the right index
• VirtualList layout reads opt out of React Compiler memoization so a cached read can't serve stale layout
• Focus moves skip stale destinations instead of aborting, so a dead ref can't strand focus
• React-hidden trees release their layout space (display none, not just alpha 0)

Developed and validated in plexinc/react-native-client against the embedded copy before
promotion; client-side integration stays in that repo until a release is cut.