a11y: WCAG 2.5.5 target sizes + 2.5.3 label-in-name fixes

Increase touch/click target sizes to meet WCAG 2.5.5 (minimum 44×44px
for navigation, 32px for admin UI controls):

- main.css / search.css: pagination buttons 2rem → min-height/min-width
  2.75rem (44px). Changed display to inline-flex for proper centering.
- admin.css: .admin-btn-sm gains min-height: 2rem (32px) and switches
  to inline-flex so the constraint is respected.
- admin.css: .admin-btn-remove (jury ✕ buttons) gains min-height: 2rem
  and inline-flex display + explicit cursor:pointer.

WCAG 2.5.3 label-in-name — jury remove buttons already had aria-label;
wrap the visible ✕ glyph in <span aria-hidden='true'> so screen readers
hear only the aria-label, not the symbol:

- templates/partials/form/jury-fieldset.php: all three ✕ occurrences
  (static PHP blocks + JS-generated innerHTML string) wrapped.

WCAG 4.1.2 / semantic HTML:
- admin/index.php: add role='toolbar' aria-label='Actions groupées' to
  the bulk-actions bar.

templates/partials/form/jury-fieldset.php

@@ -65,7 +65,7 @@ $juryIdx = max(count($juryLecteurs), 1);
                                 <input type="checkbox" name="jury_lecteurs_ext[0]" value="1"> Externe
                             </label>
                             <button type="button" class="admin-btn-remove" onclick="removeJuryRow(this)"
-                                    aria-label="Supprimer ce lecteur">✕</button>
+                                    aria-label="Supprimer ce lecteur"><span aria-hidden="true">✕</span></button>
                         </div>
                         <?php else: ?>
                             <?php foreach ($juryLecteurs as $li => $lm): ?>
@@ -77,7 +77,7 @@ $juryIdx = max(count($juryLecteurs), 1);
                                            <?= $lm['is_external'] ? 'checked' : '' ?>> Externe
                                 </label>
                                 <button type="button" class="admin-btn-remove" onclick="removeJuryRow(this)"
-                                        aria-label="Supprimer ce lecteur">✕</button>
+                                        aria-label="Supprimer ce lecteur"><span aria-hidden="true">✕</span></button>
                             </div>
                             <?php endforeach; ?>
                         <?php endif; ?>
@@ -97,7 +97,7 @@ $juryIdx = max(count($juryLecteurs), 1);
                           + '<label class="admin-checkbox-label admin-jury-ext">'
                           + '<input type="checkbox" name="jury_lecteurs_ext[' + juryIdx + ']" value="1"> Externe'
                           + '</label>'
-                          + '<button type="button" class="admin-btn-remove" onclick="removeJuryRow(this)" aria-label="Supprimer ce lecteur">✕</button>';
+                          + '<button type="button" class="admin-btn-remove" onclick="removeJuryRow(this)" aria-label="Supprimer ce lecteur"><span aria-hidden="true">✕</span></button>';
             list.appendChild(div);
             juryIdx++;
         }