css: replace presentational class selectors with semantic element selectors

Replace 6 CSS class selectors across tfe.css, main.css, and search.css with
semantic element-based selectors, removing the corresponding classes from the
HTML templates entirely.

tfe.css:
- .tfe-meta-list → article dl / article dl > div / article dl dt / article dl dd
- .tfe-media-block → aside figure (+ img, video, embed children)
- .tfe-file-caption → aside figcaption

main.css:
- .card__media → .home-body figure (+ img/video children and hover/motion rules)
- .card__caption → .home-body li > a > p

search.css:
- .repertoire-col > h2 → .repertoire-index section > h2

Template changes:
- tfe.php: removed class= from <dl>, <figure>, and <figcaption>
- index.php: removed class= from <figure> and <p class=card__caption>;
  stripped orphaned card__media from the gradient <div> (only --gradient needed)

No visual change — selectors match the same elements as before since the
semantic HTML was already in place from prior refactoring work.

public/assets/css/search.css

@@ -52,7 +52,7 @@
   border-right: none;
 }
 
-.repertoire-col > h2 {
+.repertoire-index section > h2 {
   font-size: 0.72rem;
   letter-spacing: 0.1em;
   text-transform: uppercase;