feat(seo): index blog tag and author archive routes (#197)

[Escelit]

Closes #197

/blog/tag/* and /blog/author/* were served by the app but rejected by isIndexableRoute, so they had no sitemap entries and no metadata.
The root cause was that blogSlugFrom matched any /blog/, swallowing tag and author paths before they could be handled.

Policy

Route family	Indexable?	Condition
/blog/tag/:slug	✅	slug maps to a tag in blog-manifest.json
/blog/author/:id	✅	author has optIn: true and is not opted out
unknown tag slug	❌	returns null / not in sitemap
opted-out / unknown author	❌	returns null / not in sitemap

Changes

• og-metadata.ts — blogSlugFrom narrowed to single-segment paths; new tag/author helpers; isIndexableRoute, resolveRouteMetadata,
  ogImageSlugFor, listOgImageJobs all updated
• blog-manifest.json — tags field added; gen-blog-manifest.mjs emits it going forward
• en/es/pt.json — ogContent extended for all 7 known tags and the lena-vogt author archive

Tests — 23 new tests; all 105 og-metadata and 67 middleware tests pass. Build generates 99 OG images across 33 routes.

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[truthixify]

The non-indexed tag policy is not fully emitted in the rendered page. In src/pages/Blog.tsx:479, the unknown-tag branch sets only the title; unlike the unknown/opted-out author branch, it does not add <meta name="robots" content="noindex" />. The middleware deliberately bypasses /blog/tag/nonexistent-tag, so the base HTML also has no noindex directive. This leaves an unknown tag archive without the robots policy required by #197.

Please add the noindex directive to the unknown-tag state and cover the rendered unknown tag route in a test. Known tag metadata, sitemap entries, OG generation, and the focused build all passed locally.