Harden blog author avatar resolution and add CI audit

[vibemarketerpromax]

Summary

• improve Notion author image extraction with robust property matching (case-insensitive + fuzzy keys)
• support author image URL extraction from files/url/rich_text properties
• add fallback to Notion Author people avatar_url when explicit author image field is missing
• add richer diagnostics for author image cache/download failures with slug + author + source context
• add authors:audit script to validate published Notion posts have author images (explicit or people avatar)
• wire authors:audit into CI after build to catch missing avatars before merge

Files

• lib/notion-blog.ts
• lib/notion-image-cache.ts
• scripts/audit-author-avatars.mjs
• package.json
• .github/workflows/ci.yml

Validation

• npm run typecheck
• npm run lint (existing warnings only)
• npm run build
• npm run authors:audit (skips without NOTION_TOKEN locally; enforced in CI with secret)