Follow Products.description consolidation to richText-only

Backend dropped the plain-text description field in favor of a single
richText one (see docker/payload commit 1ba8d07). Renders formatted
(bold/italic/multiple paragraphs) via the shared RichText component on
the PDP (der-eine, tasse-die-pause); everywhere else (Passend-dazu cards,
Product JSON-LD, homepage spotlight fallback) derives plain text at read
time via a new extractPlainText() helper instead of a second field.
Removes the description line from cart line items entirely — it only
bloated the cart with no real benefit there.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J1Hu5bZ1kZUgKhab6yNwCt

app/cart/components/CartContent.tsx

@@ -276,7 +276,6 @@ export function CartContent({
                         equal-height pressure from neighboring lines, so a
                         plain conditional line is enough here. */}
                     {lowStock && <p className="text-label font-bold text-warning">Nur noch wenige verfügbar</p>}
-                    <p className="font-bold text-body-sm text-text-muted">{product.description}</p>
                     <div className="flex flex-col gap-0.5 items-start">
                       <p className="text-label text-text-muted">Einzelpreis</p>
                       <p className="flex items-baseline gap-1.5">