fix: harden booking and meeting flows

app/(payload)/api/meetings/[slug]/register/route.ts

@@ -38,6 +38,7 @@ export async function POST(request: Request, { params }: Args) {
   let body: { name?: unknown; email?: unknown };
   try {
     body = await request.json();
+    if (!body || typeof body !== "object" || Array.isArray(body)) throw new Error("Invalid body");
   } catch {
     return NextResponse.json({ error: "Ungültige Anfrage." }, { status: 400 });
   }