docs: consolidate design change logs and refresh stale docs

features/seo_sites_articles_integration.feature

@@ -8,7 +8,7 @@ Feature: SEO round, slice 4: Sites defaults, Articles search status, Integration
 
   Background:
     Given the screens are SitesView (/settings/sites), ArticleView (/article, also reached as /articles), IntegrationView (/integration) and the Editor SEO panel (/article/:id/edit), inside DashboardShell, per docs/design/routes.md
-    And the visual spec of record is docs/design/screens/sites.md ("Sites: SEO defaults", 5 states), articles.md ("Articles: search status", 3 states), integration.md ("Search and sharing"), editor.md (SuggestionList), docs/design/components.md (SeoStatusChip, SuggestionList), docs/design/seo-slices.md and docs/design/states.md ("SEO round"). Exact copy is read from those files and is not repeated here unless a scenario needs it
+    And the visual spec of record is docs/design/screens/sites.md ("Sites: SEO defaults", 5 states), articles.md ("Articles: search status", 3 states), integration.md ("Search and sharing"), editor.md (SuggestionList), docs/design/components.md (SeoStatusChip, SuggestionList), docs/design/decisions.md and docs/design/states.md ("SEO round"). Exact copy is read from those files and is not repeated here unless a scenario needs it
     And the board frames of docs/design/source/DirectoryFrame.dc.html (Sites form, SuggestionList), AppFrame.dc.html (Articles rows, cards and toolbar) and IntegrationPage.dc.html (group and index) are the layout tiebreaker
     And this slice is SPA only and uses the API of features/seo_data_backend.feature and features/seo_output_backend.feature, plus counts.suggestions added by features/articles_pagination_api.feature. No other Go file changes
     And the SPA calls, with relative URLs through useApi only: GET /v1/site/, POST /v1/site/ and PATCH /v1/site/{id} (site_name, title_template, default_description), GET /v1/article/ with the optional seo=suggestions parameter, whose response also carries counts.suggestions, and PATCH /v1/article/{id} with seo_dismissed. The Integration page makes no request