feat: SEO backend output (2/4)

docs/release-notes.md

@@ -35,6 +35,13 @@ Articles and sites now store the data a website needs for search and sharing, an
 - Changed: `GET /v1/media/{id}/usage` stays an array, and every item gains `type` and `fields` without losing `id`, `title` and `published`. Authors and sites that use the image are now listed, without a `published` key.
 - Changed: a cover image, a social image, an author avatar and a site default social image all count in `used_in` and in the `unused` filter. Deleting an image clears the covers and social images that use it, and merging or purging repoints them.
 
+### New: SEO output
+
+- `GET /v1/article/{id}/seo` returns the resolved search and sharing data of an article (title with the site template, description, canonical address, robots, Open Graph, Twitter, image, authors and ready JSON-LD), so a frontend can render its meta tags without reimplementing the fallback chain. Drafts answer verified callers only.
+- `POST /v1/article/{id}/seo/check` evaluates an article without saving, with optional overrides, and reports the suggestions, the status and whether the slug is free.
+- `GET /v1/article/` items carry `seo_status` and `seo_suggestions`, and the new `seo` parameter filters on the status.
+- `GET /v1/site/{key}/sitemap` lists the published URLs of a site, paged, with the total in `X-Total-Count`, which is now exposed to browsers through CORS.
+
 ### Upgrading
 
 - The first start after the upgrade adds the new columns, gives every existing article a slug generated from its title (in id order within each site, with `-2`, `-3` on conflicts) and creates the unique `(site_id, slug)` index. Nothing else changes, and a second start changes nothing.