feat(morph): add prepared DOM targets

[alowpoly]

Summary

• add and publicly export createPolyMorphPreparedDomTarget and its public types
• accept the empty transform string as identity and deduplicate writes against JavaScript-tracked requested values
• certify runtime and declaration exports from the packed consumer
• preserve existing validation, package configuration, and typesVersions

Validation

• pnpm --filter @layoutit/polycss-morph test
• pnpm --filter @layoutit/polycss-morph test:coverage
• pnpm --filter @layoutit/polycss-morph test:package
• pnpm test
• pnpm build