Build HTML accessibility audit module

Create a TypeScript module that audits an HTML string for educational content accessibility issues. The function should:

auditAccessibility(html: string): AuditResult

Check for:

• Missing or empty alt text on images
• Improper heading hierarchy (h1 -> h3 skipping h2)
• Missing lang attribute
• Low contrast text (parse inline styles)
• Images of text (detect common patterns)
• Missing table headers
• Links with non-descriptive text ("click here", "read more")

Return structured results: { score: number (0-100), issues: Array<{ rule: string, severity: 'error'|'warning', element: string, suggestion: string }> }

Include tests with sample HTML containing various accessibility issues.