admin: semantic HTML pass — checkbox fieldset, landmarks, dl/dt, autocomplete, inline styles

checkbox-list.php partial:
- Replace outer <div>/<label> with <div>/<span class="admin-row-label"> + inner
  <fieldset class="admin-checkbox-group"><legend class="sr-only"> to satisfy
  WCAG 1.3.1 (group label for multi-checkbox rows without duplicating visible text)
- Replace <div class="admin-checkbox-list"> with <ul>; each checkbox wrapped in <li>

admin.css:
- Drop .admin-checkbox-list; add .admin-body fieldset.admin-checkbox-group rules
  (border/padding reset so it doesn't inherit jury-fieldset box styling)
- Extend form-row label rule to span.admin-row-label
- .admin-inline-form + .admin-inline-form { margin-top:.35rem } replaces inline style
- .admin-input--inline / .admin-select--inline get width:160px (was inline style)
- .admin-tags-count + table th sizing via :has() replaces th inline styles

login.php: wrap content in <main id="main-content"> (missing landmark)

account.php:
- <div class="admin-account-status"> → <dl>; __label <span> → <dt>
- <div class="admin-danger-zone__description"> → <p>

index.php: <div class="admin-maintenance-bar"> → <aside role="status" aria-label="Statut du site">

add.php / edit.php: autocomplete="name" on author field, autocomplete="email" on
contact field (WCAG 1.3.5 / input purpose)

tags.php: all inline style= attributes removed (width, text-align, margin-top,
display:inline); all moved to CSS classes

public/assets/css/admin.css

@@ -54,7 +54,8 @@
   border-bottom: 1px solid var(--border-primary);
 }
 
-.admin-form > div:not(.admin-submit-wrap) > label {
+.admin-form > div:not(.admin-submit-wrap) > label,
+.admin-form > div:not(.admin-submit-wrap) > span.admin-row-label {
   font-size: 0.92rem;
   padding-top: 0.5rem;
   font-weight: 400;
@@ -140,12 +141,28 @@
   display: block;
 }
 
-/* Checkboxes */
-.admin-checkbox-list {
+/* Checkbox group fieldset (languages, formats)
+   Wraps the <ul> of checkboxes; the visible label is a sibling <span>
+   in the grid row. The <legend> repeats the label text for AT only (sr-only).
+   .admin-body scope ensures this overrides the generic .admin-body fieldset rule. */
+.admin-body fieldset.admin-checkbox-group {
+  border: none;
+  padding: 0;
+  margin: 0;
+  background: transparent;
+}
+
+.admin-body fieldset.admin-checkbox-group > ul {
+  list-style: none;
+  margin: 0;
+  padding-top: 0.3rem;
   display: flex;
   flex-direction: column;
   gap: 0.35rem;
-  padding-top: 0.3rem;
+}
+
+.admin-body fieldset.admin-checkbox-group > ul > li {
+  display: contents; /* let the inner label handle layout */
 }
 
 .admin-checkbox-label {
@@ -754,13 +771,26 @@
 .admin-input--inline,
 .admin-inline-form input[type="text"] {
   font-size: 0.82rem;
+  width: 160px;
 }
 
 .admin-select--inline,
 .admin-inline-form select {
   font-size: 0.82rem;
+  width: 160px;
 }
 
+/* Stack secondary forms (merge, delete) below the rename form */
+.admin-inline-form + .admin-inline-form {
+  margin-top: 0.35rem;
+}
+
+/* Tags table column sizing */
+.admin-body table:has(.admin-tags-count) th:nth-child(1) { width: 40%; }
+.admin-body table:has(.admin-tags-count) th:nth-child(2) { width: 12%; }
+.admin-body table:has(.admin-tags-count) th:nth-child(3) { width: 48%; }
+.admin-tags-count { text-align: center; }
+
 /* ── Banner preview ─────────────────────────────────────────────────────── */
 .admin-banner-preview img {
   max-width: 320px;