Add /widerruf and /agb legal pages, fix newsletter modal scroll jank

- New /widerruf page: CMS-driven content via getLegalPage("widerruf"),
  sidebar TOC + "Nachhaltig handeln" callout, TrustRow, and a download
  card for the Muster-Widerrufsformular PDF attachment.
- New /agb page, same legal-page shell pattern as Impressum/Datenschutz.
- lib/payload.ts: getLegalPage now also resolves the optional `attachment`
  media relation (depth=1) for legal pages that have a downloadable file.
- NewsletterModal: replaced the body overflow/position scroll-lock hacks
  (which fought with the sticky Navbar and the global scroll-smooth CSS)
  with a wheel/touch event interceptor that never touches scroll position
  at all, plus `preventScroll: true` on all modal/drawer focus() calls to
  stop the browser's implicit scrollIntoView from nudging the page for
  elements near the sticky navbar's reserved scroll-padding-top zone.
  Same preventScroll fix applied to VersandModal and the Navbar mobile
  drawer for consistency.
- globals.css: scrollbar-gutter: stable, so a modal's overflow:hidden
  lock never causes a scrollbar-width layout shift.
- Divider: stagger its reveal animation slightly (delay 0.3s) behind the
  section above it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/lib/payload.ts

@@ -119,18 +119,21 @@ export type LegalPage = {
   type: LegalPageType;
   title: string;
   content: unknown;
+  attachment: { url: string; title: string } | null;
 };
 
 type PayloadLegalPage = {
   type: LegalPageType;
   title: string;
   content: unknown;
+  attachment: { url: string; title: string } | number | null;
 };
 
 export async function getLegalPage(type: LegalPageType): Promise<LegalPage | null> {
   const params = new URLSearchParams({
     "where[tenant.slug][equals]": TENANT_SLUG,
     "where[type][equals]": type,
+    depth: "1",
     limit: "1",
   });
 
@@ -145,5 +148,13 @@ export async function getLegalPage(type: LegalPageType): Promise<LegalPage | nul
   const data: { docs?: PayloadLegalPage[] } = await res.json();
   const doc = data.docs?.[0];
   if (!doc) return null;
-  return { type: doc.type, title: doc.title, content: doc.content };
+  return {
+    type: doc.type,
+    title: doc.title,
+    content: doc.content,
+    attachment:
+      typeof doc.attachment === "object" && doc.attachment
+        ? { url: doc.attachment.url, title: doc.attachment.title }
+        : null,
+  };
 }