site: ui/ux refresh, seo pass, find/lists indexes, 25 new finds

- newspaper-style masthead (stats | "Unique" | About/Blog) on every page
  with per-page italic subheader + last-updated date on listing pages;
  sitewide 42rem reading width
- pinterest home (hero + masonry, "load more"); old list view at /index3/
- new pages: /about, /blog, /legal, /find/, /finds/, custom 404
- footer collection links now clickable; "founded" stat replaces "updated"
  in the masthead
- centralised SEO component with per-page json-ld (Review, BlogPosting,
  Product, Article, CollectionPage, ItemList, BreadcrumbList, etc.);
  @astrojs/sitemap + @astrojs/rss; robots.txt; promoted finds canonical
  to their review
- memoize getSiteStats() so the masthead/footer counts don't multiply
  per-page build cost
- 25 new daily-finds captures

public/robots.txt

@@ -0,0 +1,4 @@
+User-agent: *
+Allow: /
+
+Sitemap: https://unique.rzen.dev/sitemap-index.xml