feat(website): add PDF to Markdown answers

[Natsummerance]

Summary

• Add dedicated localized answer pages for the high-intent PDF to Markdown task in English, Simplified Chinese, Traditional Chinese, and Japanese.
• Expose unique canonical URLs, hreflang sets, FAQPage/HowTo/Breadcrumb structured data, PNG social metadata, internal links, and visible workflows.
• Extend root and localized AI corpora plus sitemap from 32 to 36 canonical URLs.
• Expand browser smoke and clean-network production checks to all 36 routes.

Approvals

• SEO intent: 9.89
• Content accuracy: 9.83
• Release engineering: 9.79
• Final decision meeting: 9.84 (pdf_answer_pages_approval.json)

Validation

• npm run verify:release: green across 36 canonical URLs.
• Browser smoke: 36 / 36 routes passed, including four new PDF pages; zero failures and zero broken images.
• Production workflow now covers all twelve localized PDF route variants.