Fix “HTML content in description” on Google Merchant Center

HTML in description doesn't render as formatting; the raw tags display in some surfaces and break layout. Plain text only — paragraphs separated by newlines, no markup beyond basic punctuation.

The exception is Shopify and similar platforms where descriptions are stored with HTML for storefront rendering. The feed-generation step needs to strip HTML before output. Standard HTML-to-plain-text conversion handles this; many feed tools do it automatically but some pipelines miss the step.

For description content needing visual structure (bullet points, headings), use the product_highlight field or rely on the description's plain-text paragraph breaks. Don't try to encode visual structure in description itself.