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.

public/assets/css/main.css

@@ -193,9 +193,9 @@
   display: inline-flex;
   align-items: center;
   justify-content: center;
-  min-width: 2rem;
-  height: 2rem;
-  padding: 0 0.5rem;
+  min-width: 2.75rem;
+  min-height: 2.75rem;
+  padding: 0 0.6rem;
   border: 1px solid var(--border-secondary);
   border-radius: 3px;
   color: var(--text-primary);