Build HTML accessibility audit module

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