feat: public API, SEO and existing surfaces

docs/llms.md

@@ -20,3 +20,7 @@ All of them are public. `{{VERSION}}` and `{{BASE_URL}}` in the sources are repl
 - Recipes in `docs/llm/` hold real responses. Re-capture them when a response shape changes.
 
 `TestRouterRoutesAreInTheCatalogue` fails when a route of `api/router.go` is missing from the catalogue. Routes still undocumented are listed in `routesNotYetInTheCatalogue` in `test/api_catalogue_drift_test.go`; remove an entry once the route is documented.
+
+## Languages in the generated output
+
+The article object carries `lang` and `story_id`, and the public language routes `GET /v1/public/site/{key}/lang/{lang}/article/{slug}` and `GET /v1/public/site/{key}/story/{story_id}` return `alternates` and, for the second, `requested_lang` and `fallback`. They are described in `docs/api/article-localization.md`, in the catalogue and in the recipes, so `/llms-full.txt` and `/openapi.json` include them after `task build:llms`.