Add auto-updating sitemap.xml and robots.txt

Sitemap combines hardcoded static routes with Payload's Pages and
published Posts collections (hourly ISR revalidation), so new CMS
pages/blog posts appear without a code change. Excludes noindex
transactional routes (checkout, cart, bestellbestaetigung,
newsletter-confirmed, konto/*) to avoid Search Console warnings.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013Eg6h91yngXmSnM51wxXM8

app/lib/payload.ts

@@ -1518,3 +1518,46 @@ export async function getPageBySlug(slug: string, options?: { draft?: boolean })
   if (!doc) return null;
   return mapPayloadPage(doc);
 }
+
+export type SitemapEntry = { slug: string; updatedAt: string };
+
+// Backs app/sitemap.ts. Pages has no status/draft field (see Pages.ts) —
+// every doc that exists is live — so unlike getBlogPosts there's no
+// `where[status]` filter needed here.
+export async function getAllPageSlugs(): Promise<SitemapEntry[]> {
+  const params = new URLSearchParams({
+    "where[tenant.slug][equals]": TENANT_SLUG,
+    depth: "0",
+    limit: "100",
+  });
+
+  const res = await fetch(`${PAYLOAD_URL}/api/pages?${params}`, { next: { revalidate: 3600 } });
+  if (!res.ok) {
+    console.error(`getAllPageSlugs: Payload returned ${res.status} ${res.statusText}`);
+    return [];
+  }
+
+  const data: { docs?: { slug: string; updatedAt: string }[] } = await res.json();
+  return (data.docs ?? []).map((doc) => ({ slug: doc.slug, updatedAt: doc.updatedAt }));
+}
+
+// Same shape as getAllPageSlugs but for Posts, which — unlike Pages — does
+// have a draft/scheduled state, so this filters to `published` the same
+// way getBlogPosts does (the sitemap must never list a post that 404s).
+export async function getAllPostSlugs(): Promise<SitemapEntry[]> {
+  const params = new URLSearchParams({
+    "where[tenant.slug][equals]": TENANT_SLUG,
+    "where[status][equals]": "published",
+    depth: "0",
+    limit: "100",
+  });
+
+  const res = await fetch(`${PAYLOAD_URL}/api/posts?${params}`, { next: { revalidate: 3600 } });
+  if (!res.ok) {
+    console.error(`getAllPostSlugs: Payload returned ${res.status} ${res.statusText}`);
+    return [];
+  }
+
+  const data: { docs?: { slug: string; updatedAt: string }[] } = await res.json();
+  return (data.docs ?? []).map((doc) => ({ slug: doc.slug, updatedAt: doc.updatedAt }));
+}