Implement Release 3 site auditing

[alianjum0]

Summary

• add bounded same-origin sitemap auditing for up to 10 pages
• report duplicate metadata and JSON-LD validity/types
• expose HTML and JSON site-audit results with responsive presentation
• reuse existing SSRF-safe fetch boundaries and safe error handling

Validation

• rtk pnpm run verify
• 61 tests passed, 0 failed
• syntax checks passed
• no known production dependency vulnerabilities
• desktop and 390x844 browser checks passed with no console errors
• rtk proxy git diff --check

Risks and limits

• intentionally limited to 10 pages, three child sitemaps, and one sitemap-index level
• JSON-LD checks syntax and declared types, not full Schema.org compliance
• no deployment is included