TKW: resolve repository audit findings

[codebend3r]

Summary

• Add repository-wide content integrity validation — duplicate slugs, filename/frontmatter mismatches, broken cross-collection references
• Contain keyboard focus within the site menu by exposing it as a modal dialog
• Replace the vulnerable content-parser dependencies and clear bun audit
• Refresh the README to match the current stack, routes, and deployment

Content integrity

• New lib/content-integrity.ts validates unique slugs, filename-vs-frontmatter slugs, and links across collections
• Correct malformed and stale entity references
• Add placeholder records for referenced-but-unwritten characters
• Broken links now fail tests with source and field diagnostics

Accessibility

• Expose the open SiteMenu drawer as a modal dialog
• Loop forward and reverse tab focus within its controls

Security

• Replace gray-matter / js-yaml 3 with the maintained yaml parser
• Override Next's vulnerable transitive PostCSS pin
• Retain frontmatter parsing coverage; bun audit --prod reports no vulnerabilities

Docs

• Document the Bun workflow, routes, and project layout
• Document content integrity and placeholder conventions
• Explain static export and Netlify deployment

[netlify]

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