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/tfe.php

@@ -79,7 +79,7 @@ $bodyClass = 'tfe-body';
 
                 <p class="tfe-author"><?= htmlspecialchars($data['authors'] ?? 'Auteur inconnu') ?></p>
 
-                <dl class="tfe-meta-list">
+                <dl>
                     <?php if (!empty($data['orientation'])): ?>
                     <div>
                         <dt>Orientation :</dt>
@@ -204,7 +204,7 @@ $bodyClass = 'tfe-body';
                 <?php elseif (!empty($data['files'])): ?>
                     <?php foreach ($data['files'] as $file): ?>
                         <?php $ext = strtolower(pathinfo($file['file_path'], PATHINFO_EXTENSION)); ?>
-                        <figure class="tfe-media-block">
+                        <figure>
                             <?php if ($ext === 'pdf'): ?>
                                 <embed src="/media.php?path=<?= urlencode($file['file_path']) ?>"
                                        type="application/pdf" width="100%" height="700px">
@@ -226,7 +226,7 @@ $bodyClass = 'tfe-body';
                                 </video>
                             <?php endif; ?>
                             <?php if (!empty($file['description'])): ?>
-                                <figcaption class="tfe-file-caption"><?= htmlspecialchars($file['description']) ?></figcaption>
+                                <figcaption><?= htmlspecialchars($file['description']) ?></figcaption>
                             <?php endif; ?>
                         </figure>
                     <?php endforeach; ?>