feat(native): add cross-platform renderer foundation

[bntvllnt]

Summary

• add framework-free @vllnt/ui-core tokens, native themes, platform types, and portable contracts generated from packages/design
• add experimental @vllnt/ui-native Button, Text, Heading, Badge, and Card renderers plus a private Expo catalog that bundles on Android and iOS
• make registry pages, JSON, search, JSON-LD, llms surfaces, and MCP platform-aware while preserving the stable @vllnt/ui web package
• add native CI and a separately gated, canary-only synchronized publishing workflow

Scope

This PR implements the native renderer, shared-token/contract, registry, CI, and release-boundary portion of #479. Hook extraction and Tailwind preset consolidation remain separate follow-up work.

@vllnt/ui remains byte-for-byte unchanged across its manifest, source tree, CSS, and theme files. Native packages are experimental and publication remains disabled until maintainers provision npm trusted publishers, create the protected npm-native-canary environment, and set NATIVE_CANARY_PUBLISH_ENABLED=true.

Verification

• pnpm install --frozen-lockfile
• pnpm lint
• pnpm -F @vllnt/ui exec tsc --noEmit --project tsconfig.build.json
• pnpm build
• pnpm test:once — 318 web test files / 1,671 web tests plus core, native, catalog, and registry tests
• pnpm check:circular
• pnpm ci:native — package boundaries, packed artifacts, Expo Doctor 21/21, Android + iOS Metro exports
• pnpm -F @vllnt/ui-registry registry:check
• pnpm -F @vllnt/ui-registry registry:integrity
• pnpm -F @vllnt/ui-registry i18n:check
• pnpm -F @vllnt/ui-registry exec playwright test e2e/platforms.spec.ts — 3 passed
• CI=1 pnpm -F @vllnt/ui-registry exec playwright test e2e/i18n.spec.ts — 44 passed
• React Doctor staged scan — no errors
• dependency audit comparison — no new high-severity advisory versus origin/main; Expo's ws path is pinned to 8.21.3
• git diff --check

Review notes

• Full Playwright CT was attempted, but the repository currently tracks baselines for only a small subset of the 309 web components; 37 cases passed and baseline-less cases failed. No web package implementation or style files change in this PR.
• Native destructive-label contrast is generated and tested at WCAG AA. Native dark background uses near-black rather than pure black.
• No merge or package publication is requested by this draft.

Related to #479

[vllnt-pilot]

ntk preview

App	Status	Preview
ui-registry	Ready	https://pr-506-ui-registry.preview.vllnt.ai
storybook	Skipped (preview cell not configured)	—

Built from f1e04d36 · public + no-index (ADR-082) · torn down on close