feat: vue-seo-layer, the Nuxt half of the SummerCMS SEO plugin

app/plugins/seo-head.ts

@@ -0,0 +1,14 @@
+// One head entry for the whole app, following the resolve answer of the
+// current page. tagPriority 'critical' makes its tags win over the same
+// tags a page or another module sets (unhead keeps the lower weight), so
+// editor values from the SEO plugin override the content defaults; a value
+// the answer lacks leaves the page's own tag in place.
+
+import { seoHeadInput } from '../utils/seo.ts'
+
+export default defineNuxtPlugin(() => {
+  const config = useRuntimeConfig()
+  if ((config.public.seo as { enabled?: boolean } | undefined)?.enabled === false) return
+  const answer = useSeoAnswer()
+  useHead(computed(() => seoHeadInput(answer.value)), { tagPriority: 'critical' })
+})