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/components/Divider.tsx

@@ -25,7 +25,10 @@ function Arrow() {
 
 export function Divider() {
   return (
-    <Reveal className="flex items-center justify-center flex-wrap gap-x-8 gap-y-3 pb-5 pt-12 px-[var(--layout-padding-x)] w-full bg-bg-base text-center">
+    <Reveal
+      delay={0.3}
+      className="flex items-center justify-center flex-wrap gap-x-8 gap-y-3 pb-5 pt-12 px-[var(--layout-padding-x)] w-full bg-bg-base text-center"
+    >
 
       {/* Word + its trailing icon are grouped into one shrink-0 flex unit
           so flex-wrap only ever breaks BETWEEN pairs, never leaving an