Export and document “Style Tokens” programmatically

Releases reference renaming/adding style tokens. Please export a typed tokens object (e.g., `import { tokens } from 'vue-doxen/style-tokens'`) and document it, so consumers can build theme tooling. Why Avoid drift between docs and actual tokens; enable IDE autocompletion and internal linting. Acceptance Add an export with a stable API Mention it in docs + changelog when tokens change Context RC 41 mentions style token rename (`doxenPlainText` → `plainText`) and a missing token being added. A formal API would help consumers adapt.