Wire testimonials CMS collection and Payload Live Preview

Testimonials on /todo-cards, /newsletter, /challenge now come from the new
Payload testimonials collection via a shared TestimonialsGrid component,
instead of 3 separately hardcoded arrays.

Adds Next.js Draft Mode (/api/preview) plus Live-Preview-aware client
wrappers (LiveRichText, LiveTestimonialsGrid, LivePostContent) for posts,
legal pages, and testimonials — mounted only while Draft Mode is enabled,
so ordinary visitors keep getting the plain static components.

app/datenschutz/page.tsx

@@ -1,9 +1,11 @@
 import type { Metadata } from "next";
 import Link from "next/link";
 import Image from "next/image";
+import { draftMode } from "next/headers";
 import { Reveal } from "../components/Reveal";
 import { Footer } from "../components/Footer";
 import { RichText, extractHeadings } from "../components/RichText";
+import { LiveRichText } from "../components/LiveRichText";
 import { SectionTOC } from "../components/SectionTOC";
 import { getLegalPage } from "../lib/payload";
 
@@ -16,6 +18,7 @@ export const metadata: Metadata = {
 export default async function DatenschutzPage() {
   const page = await getLegalPage("datenschutz");
   const headings = page ? extractHeadings(page.content) : [];
+  const { isEnabled: isPreview } = await draftMode();
 
   return (
     <>
@@ -60,7 +63,7 @@ export default async function DatenschutzPage() {
 
           <div className="w-full lg:flex-1 min-w-0">
             {page ? (
-              <RichText content={page.content} />
+              isPreview ? <LiveRichText initialContent={page.content} /> : <RichText content={page.content} />
             ) : (
               <p className="text-body text-text-muted">Inhalte werden gerade aktualisiert.</p>
             )}