Add /impressum and /datenschutz pages backed by Payload

- lib/payload.ts: getLegalPage(type) alongside the existing
  getBlogPosts/getProducts fetchers
- New RichText component: small dependency-free Lexical JSON → JSX
  renderer for Payload's richText fields (headings get stable
  "section-N" ids for anchor/TOC linking)
- New SectionTOC: generalized from VersandTOC into a reusable
  scroll-spy sidebar driven by any {id, title}[] — Datenschutz needs one
  built from CMS-authored headings, not a hardcoded array. VersandTOC is
  now a thin wrapper around it. Sticky positioning moved from the nav
  itself to each page's sidebar wrapper, so a TOC and an extra card
  (Impressum/Datenschutz both have one) scroll together as one unit
  instead of the card drifting away independently
- TOC clicks set the active item immediately and hold it for ~1s over
  the scroll-spy observer, covering both "target already fully visible,
  nothing to scroll" and "an unrelated section flickers through the
  intersection band mid-scroll"
- Both pages follow the same breadcrumb+H1+TOC-sidebar+content layout
  established for /versand

app/versand/page.tsx

@@ -34,7 +34,9 @@ export default function VersandPage() {
         </Reveal>
 
         <div className="flex flex-col lg:flex-row gap-8 lg:gap-12 items-start pb-16 pt-2 px-[var(--layout-padding-x)] w-full">
-          <VersandTOC />
+          <div className="hidden lg:block lg:sticky lg:top-32 lg:self-start">
+            <VersandTOC />
+          </div>
           <div className="w-full lg:flex-1 max-w-[45rem]">
             <VersandSections withAnchors />
           </div>