remove listing hero remnants

[LjyYano]

What changed

• remove unused category kicker metadata from all six category pages
• remove CSS that was only used by the deleted archive and category hero blocks
• remove the English quote from the About page
• keep category descriptions for page metadata and SEO

Why

The visible hero blocks were already removed from the listing templates. This follow-up removes their remaining data and styling so the deleted presentation cannot linger in the codebase.

Validation

• all category front matter parses successfully
• About page passes strict Liquid 4 parsing
• no listing-hero, listing-title-row, or category kicker references remain
• git diff --check passes