fix(seo): align social metadata with blog covers

[drewstone]

What changed

• Normalize the 14 editorial WebP covers to 1200×630 for predictable social previews.
• Emit og:image:type from the actual file extension, so WebP covers are labeled image/webp.

Proof

• pnpm check:blog — 85 posts, 13 series, 0 errors, 0 warnings.
• pnpm build — passed and prerendered all blog routes.
• git diff --check — passed.
• file public/images/covers/editorial/*.webp — all 14 assets are 1200×630 WebP.

This follows the merged reader-first content pass and keeps the page hero, structured data, and social metadata on the same cover asset.

[tangletools]

✅ Auto-approved drewstone PR — 780d1ea3

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-08-03T07:28:30Z}