Fix biome lint errors: remove duplicate CSS properties, apply safe auto-fixes

CSS:
- Remove duplicate 'background' fallbacks in base.css, header.css, search.css
  (solid color declared before gradient — gradient always wins)
- Remove duplicate 'padding' in admin.css .admin-import-log

JS (biome --write safe fixes applied):
- function() → arrow functions in all IIFEs and callbacks
- forEach/callback → arrow functions
- evaluePtrn → parseInt(x, 10) in admin-contacts-form.js
- Cleaned label text in build.mjs lint step

Remaining warnings are intentional: !important overrides, descending
specificity (admin.css cascade), noUnusedVariables (functions exported
to window/onclick), useTemplate style preference.

app/templates/public/licence.php

@@ -4,7 +4,7 @@
     <?php if (!empty($tocItems)): ?>
     <details class="toc" open>
         <summary><?= icon('caret-down', 0, 'toc-caret') ?> PARTIES</summary>
-        <ul>
+        <ul class="toc-list">
             <?php foreach ($tocItems as $item): ?>
             <li><a href="<?= htmlspecialchars($item['href']) ?>"><?= htmlspecialchars($item['label']) ?></a></li>
             <?php endforeach; ?>
@@ -12,12 +12,12 @@
     </details>
     <?php endif; ?>
 
-    <div class="content">
+    <article>
         <?php if (!empty(trim($content))): ?>
             <?= $html ?>
         <?php else: ?>
             <p>Contenu à venir.</p>
         <?php endif; ?>
-    </div>
+    </article>
 
 </main>