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/lib/structuredData.ts

@@ -53,7 +53,7 @@ export function buildProductSchema(product: Product, url: string, seller: Compan
     "@context": "https://schema.org",
     "@type": "Product",
     name: product.name,
-    description: product.description,
+    description: product.descriptionText,
     image: product.gallery.length > 0 ? [product.image, ...product.gallery] : product.image,
     url,
     ...(product.sku ? { sku: product.sku } : {}),