docs: consolidate design change logs and refresh stale docs

features/seo_output_backend.feature

@@ -7,7 +7,7 @@ Feature: SEO output backend, resolved SEO object, non-persisting check, list sta
   So that a frontend can render meta tags and a sitemap without reimplementing the fallback chain
 
   Background:
-    Given the spec of record is docs/design/seo-slices.md (slice 2), docs/design/change-list.md ("SEO round"), docs/design/screens/editor.md, docs/design/screens/articles.md and docs/design/screens/integration.md
+    Given the spec of record is docs/design/decisions.md (Search and sharing), docs/design/screens/editor.md, docs/design/screens/articles.md and docs/design/screens/integration.md
     And this slice is backend only: no SPA screen and no change to docs/design
     And it reuses the article and site SEO fields of features/seo_data_backend.feature and adds no column and no migration
     And RenewCMS renders no page and injects no meta tag: it only returns data