feat(website): show desc-row on index page when a filter is active

On category pages desc-rows are always visible. On the index page they
were always hidden. Now they become visible whenever a tag/category
filter is applied, giving filtered results the same richness as category
pages.

Also tightens two related CSS rules: border-bottom suppression only
fires when the adjacent desc-row is actually visible, and the expand-row
description is hidden while the desc-row is already showing to avoid
duplicate text.

Co-Authored-By: Claude <noreply@anthropic.com>