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/newsletter/page.tsx

@@ -1,10 +1,13 @@
 import type { Metadata } from "next";
+import { draftMode } from "next/headers";
 import { WeeklyImpulsesHero } from "./components/WeeklyImpulsesHero";
 import { HowItWorks } from "./components/HowItWorks";
 import { WeeklyBenefits } from "./components/WeeklyBenefits";
-import { Testimonials } from "./components/Testimonials";
 import { Newsletter } from "../components/Newsletter";
 import { Footer } from "../components/Footer";
+import { TestimonialsGrid } from "../components/TestimonialsGrid";
+import { LiveTestimonialsGrid } from "../components/LiveTestimonialsGrid";
+import { getTestimonials } from "../lib/payload";
 
 const title = "Impulse & Tipps – Wöchentliche Klarheit für deinen Alltag";
 const description =
@@ -35,14 +38,21 @@ export const metadata: Metadata = {
 // card). Both point at the same underlying thing (signing up for the
 // weekly newsletter), so this page resolves both at once instead of
 // picking a new URL and leaving one of them still dangling.
-export default function NewsletterPage() {
+export default async function NewsletterPage() {
+  const testimonials = await getTestimonials("newsletter");
+  const { isEnabled: isPreview } = await draftMode();
+
   return (
     <>
       <main className="flex flex-col flex-1">
         <WeeklyImpulsesHero />
         <HowItWorks />
         <WeeklyBenefits />
-        <Testimonials />
+        {isPreview ? (
+          <LiveTestimonialsGrid testimonials={testimonials} />
+        ) : (
+          <TestimonialsGrid testimonials={testimonials} />
+        )}
         <Newsletter
           title="Wöchentliche Impulse für mehr Klarheit"
           description="Melde dich jetzt an und erhalte jeden Mittwoch neue Impulse & Tipps direkt in dein Postfach."