A08: Add explicit errorPage prop to skip structuredData on error pages

Bug: Layout used 'noindex && path !== ""' to detect error pages, but the
main page (/) with filterError (422) sets noindex=true, causing the
Dataset/CollectionPage structuredData to be included on error pages.

Fix:
- Add explicit 'errorPage' prop to Layout component
- Pass errorPage={filterError} from index.astro
- Skip structuredData when errorPage=true, regardless of noindex
- Main page with 422 error no longer includes Dataset schema
- Normal pages with noindex (e.g., /admin) still work correctly

Verification:
- Astro build: 0 errors
- Error pages (422, 503, 404) skip structuredData
- Normal pages include structuredData
- noindex still works for robots meta tag

apps/web/src/layouts/Layout.astro

@@ -19,6 +19,7 @@ const {
   noindex = false,
   image = "/og-rf4spotter.png",
   structuredData = null,
+  errorPage = false,
 } = Astro.props;
 const path = Astro.url.pathname;
 const siteUrl = import.meta.env.PUBLIC_SITE_URL || "https://rf4spotter.ru";
@@ -26,9 +27,9 @@ const canonical = new URL(path, siteUrl).toString();
 const socialImage = new URL(image, siteUrl).toString();
 const preventIndexing = noindex || path.startsWith("/admin/");
 const websiteJsonLd = { "@type": "WebSite", name: "RF4 Spotter", url: siteUrl, inLanguage: "ru" };
-// A08: Skip structuredData on error pages (noindex, 422, 503, 404)
-const hasErrorStatus = noindex && path !== "/";
-const jsonLdGraph = (structuredData && !hasErrorStatus) ? [websiteJsonLd, structuredData] : [websiteJsonLd];
+// A08: Skip structuredData on error pages (explicit errorPage prop)
+// Don't infer error from noindex alone — main page can have noindex on 422
+const jsonLdGraph = (structuredData && !errorPage) ? [websiteJsonLd, structuredData] : [websiteJsonLd];
 const jsonLd = JSON.stringify({
   "@context": "https://schema.org",
   "@graph": jsonLdGraph,