Create WCAG-compliant content transformer

Build a pipeline that transforms raw educational HTML into WCAG 2.1 AA compliant output. The transformer should:

1. Fix heading hierarchy (re-level headings to be sequential)
2. Add ARIA landmarks (navigation, main, complementary) to common page structures
3. Convert data tables to have proper th/scope attributes
4. Add skip navigation links
5. Ensure all interactive elements are keyboard accessible (add tabindex where needed)
6. Convert inline styles to semantic HTML where possible (bold -> strong, italic -> em)
7. Add language attributes based on content detection

The pipeline should be composable.each transform is a separate function that can be used independently or chained. Input and output are HTML strings. Preserve original content while enhancing structure.

Write comprehensive tests for each transformer.