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/api/preview/route.ts

@@ -0,0 +1,28 @@
+import { draftMode } from "next/headers";
+import { redirect } from "next/navigation";
+import { NextRequest } from "next/server";
+
+// Entered only via the `livePreview.url` link Payload puts in its admin
+// (posts/legal-pages/testimonials, see payload.config.ts and those
+// collections' own `admin.livePreview.url` resolvers) — enables Draft Mode
+// so the target page renders its Live-Preview-aware components (see the
+// `isPreview` checks in those pages' page.tsx), then redirects into the
+// actual page. `path` is never redirected to as-is (open-redirect risk);
+// it's validated to be an internal path first.
+export async function GET(request: NextRequest) {
+  const { searchParams } = request.nextUrl;
+  const secret = searchParams.get("secret");
+  const path = searchParams.get("path");
+
+  if (!secret || secret !== process.env.PAYLOAD_PREVIEW_SECRET) {
+    return new Response("Invalid secret", { status: 401 });
+  }
+  if (!path || !path.startsWith("/") || path.startsWith("//")) {
+    return new Response("Invalid path", { status: 400 });
+  }
+
+  const draft = await draftMode();
+  draft.enable();
+
+  redirect(path);
+}