Add blog thumbnails and per-post SEO metadata

[decofe]

Summary

• add optional blog frontmatter for metaTitle and metaDescription
• emit per-post OpenGraph/Twitter/JSON-LD metadata from those fields
• use Vocs ogImageUrl dynamic OG images for /blog/*, labeled DEV BLOG, with the blog title rendered as the hero text
• keep the marketing static build's generated metadata aligned with the same dynamic /api/og URL shape
• update the T6 post with custom meta title and description

Prompted by: @juandolealt

Verification

• pnpm exec biome check vocs.config.ts src/pages/blog/[slug].tsx src/marketing/seo.ts vite.marketing.config.ts blogs/AGENTS.md blogs/t6.md src/marketing/blogPlugin.ts src/marketing/next.d.ts src/pages/_api/api/og.tsx
• pnpm check:types
• pnpm build (completed; existing changelog fetch timed out during SSG but build exited 0)
• verified dist/public/blog/t6/index.html uses Vocs dynamic /api/og?...eyebrow=DEV+BLOG and custom T6 title/description

[vercel]

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Project	Deployment	Actions	Updated (UTC)
tempo-docs	Ready	Preview, Comment	Jun 23, 2026 7:34pm