FEAT-3: litter type+CRUD, Zucht strings, /wuerfe nested routes (retire LittersPage)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gerbil-manager-web/src/pages/WurfDetailPage.tsx

@@ -0,0 +1,10 @@
+import { de } from '../strings/de'
+
+export default function WurfDetailPage() {
+  // Fleshed out in a later FEAT-3 increment (litter workspace + Jungtier erfassen).
+  return (
+    <section className="page">
+      <h2>{de.pages.litters.title}</h2>
+    </section>
+  )
+}