Add VirtualList + supporting flex/focus/resize infrastructure

[WillsonHaw]

Summary

Adds a FlashList v1-style virtualized list component (@plextv/react-lightning-components/lists/VirtualList) and the supporting primitives needed to make it work cleanly inside the existing renderer/plugin stack.

Headline

• VirtualList — viewport derivation, scroll/focus state, recycler-pool-backed cell reuse, viewability tracking. Two layout modes decided at runtime: pinned (no flex ancestor → single source of truth from LayoutManager) and measured (flex ancestor → cells wrap in FlexRoot, report main-axis size to LayoutManager, report cross-axis to a monotonic maxContentCross viewport-fallback). Authoritative spec lives in VirtualList.md next to the source.

Supporting infrastructure

• @plextv/react-lightning — NodeResizeObserver (lazy, frameTick-driven element-size watcher), FocusManager.setFocusedChild (mark a parent's preferred focus target without yanking the active focus path — load-bearing for VL recycle-restore), new resized element event, and CanvasProps type export.
• @plextv/react-native-lightning — NativeCanvas export for embedding a Lightning canvas inside a React Native Lightning tree.
• @plextv/react-lightning-plugin-flexbox — performance refactor of YogaManager, LightningManager, and the main-thread/worker pipeline. Adds a fast-path scan in transformProps so non-flex elements skip the split-and-allocate path entirely.

Tooling

• Migrated from Biome to oxc (oxlint + oxfmt).
• Adopted pnpm catalogs for cross-package version pinning.
• Updated dependencies across the workspace.

Examples / Storybook

• New apps/react-lightning-example page: NestedListPage (vertical VL of horizontal VLs with variable row heights, demonstrates focus restoration across recycle).
• Added VirtualList.stories.tsx covering vertical/horizontal/grid/header-footer-separator/empty/padding/snap-alignment/override-layout/infinite-scroll/item-types/initial-scroll/imperative/draw-distance variants.
• Removed the old FlashList.stories.tsx and react-native-lightning-components/CellContainer + FlashList (superseded by the new VL).

Breaking Changes

1. FlashList and CellContainer removed from @plextv/react-native-lightning-components

- import { FlashList, CellContainer } from '@plextv/react-native-lightning-components';
+ import VirtualList from '@plextv/react-lightning-components/lists/VirtualList';

The old FlashList wrapper and its CellContainer were deleted entirely. Replace usages with the new VirtualList. Public API differences worth knowing:

• data, renderItem, keyExtractor, numColumns, horizontal, estimatedItemSize,
  ListHeaderComponent/ListFooterComponent/ListEmptyComponent/ItemSeparatorComponent, onScroll, onEndReached, onViewableItemsChanged, onLoad/onLayout, initialScrollIndex are equivalent.
• overrideItemLayout(layout, item, index, numColumns, extraData) — set layout.size (main-axis) and optional layout.span (multi-column). Replaces FlashList's getItemType-only hook.
• getItemType(item, index, extraData) — same role.
• style.w/style.h set viewport explicitly. contentContainerStyle carries RN-style padding + backgroundColor.
• See VirtualList.md next to the source for the authoritative model.

2. @lightningjs/renderer left beta (3.0.0-beta20 → 3.0.1)

3. @plextv/react-lightning-plugin-flexbox now exports FlexRoot, FlexBoundary, useIsInFlex (and their prop types). Flexbox is now opt-in. Just including the plugin no longer enables flexbox, you need to wrap flex boundaries with a FlexRoot component. The exported NativeCanvas component in @plextv/react-native-lightning automatically wraps the application with a FlexRoot.