feat: noindex for declared and signed-in routes

- app plugin seo-route-robots: a page whose meta sets requiresAuth: true
  gets robots noindex, nofollow, a page with seo.robots gets its value,
  a path under seo.noindexRoutes gets noindex, nofollow; meta tag above
  the CMS head entry and X-Robots-Tag during SSR, never on staging
- requiresAuth and seo added to Nuxt's page meta extraction keys
- playground /konto, /szkic and /prywatne with their smoke lines

app/plugins/seo-route-robots.ts

@@ -0,0 +1,50 @@
+// Noindex for the routes an app declares (D-23, D-21), without page code:
+//
+//   - a page whose meta sets requiresAuth: true (a signed-in or auth page)
+//     gets robots "noindex, nofollow";
+//   - a page whose meta sets seo: { robots: '...' } gets that value;
+//   - a path under seo.noindexRoutes gets "noindex, nofollow" (its route
+//     rule already sends the header; this adds the meta tag).
+//
+// The value goes into a robots meta tag that wins over the CMS's (a lower
+// tagPriority than the head plugin's 'critical') and, during SSR, into the
+// X-Robots-Tag header once the navigation is done, after the route
+// middleware. Every other page keeps the CMS robots; on staging the CMS's
+// noindex, nofollow stays. Works with the layer off too: it reads no CMS.
+
+import { isNoindex } from '../../lib/guard.ts'
+import { pageMetaRobots } from '../../lib/routes.ts'
+
+/** Wins over the CMS head entry (tagPriority 'critical', -8). */
+const ROUTE_ROBOTS_PRIORITY = -10
+
+export default defineNuxtPlugin((nuxtApp) => {
+  const config = useRuntimeConfig()
+  const declared = (config.public.seo as { noindexRoutes?: unknown } | undefined)?.noindexRoutes
+  const noindexRoutes = Array.isArray(declared) ? declared.filter((p): p is string => typeof p === 'string') : []
+  const router = useRouter()
+  const answer = useSeoAnswer()
+
+  const robotsFor = (route: { path: string; meta: Record<string, unknown> }): string | null => {
+    if (answer.value?.staging === true) return null
+    const own = pageMetaRobots(route.meta)
+    if (own) return own
+    return isNoindex(route.path, noindexRoutes) ? 'noindex, nofollow' : null
+  }
+
+  useHead(
+    computed(() => {
+      const robots = robotsFor(router.currentRoute.value)
+      return robots ? { meta: [{ name: 'robots', content: robots }] } : {}
+    }),
+    { tagPriority: ROUTE_ROBOTS_PRIORITY },
+  )
+
+  if (import.meta.server) {
+    router.afterEach((to, _from, failure) => {
+      if (failure) return
+      const robots = robotsFor(to)
+      if (robots) nuxtApp.runWithContext(() => (useResponseHeader('X-Robots-Tag').value = robots))
+    })
+  }
+})