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/public/assets/css/components/toc.css

@@ -0,0 +1,141 @@
+/* ============================================================
+   SHARED TOC — sidebar table-of-contents for admin + public pages.
+   Both use <details class="toc"> markup.
+   Public:  server-rendered links (about, charte, licence)
+   Admin:   JS-populated links (contenus, accès, paramètres — admin-toc.js)
+   ============================================================ */
+
+/* ── Shared list styles (.toc-list) ─────────────────────────────────────── */
+.toc-list,
+.toc ul {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+    display: flex;
+    flex-direction: column;
+    gap: var(--space-3xs);
+}
+
+.toc-list a,
+.toc ul a {
+    display: block;
+    font-family: var(--font-body);
+    font-size: var(--step-0);
+    font-weight: 300;
+    color: var(--text-primary);
+    text-decoration: none;
+    padding: var(--space-3xs) 0;
+    transition: color 0.15s;
+}
+
+.toc-list a:hover {
+    color: var(--accent-primary);
+}
+
+.toc-list a.toc-active,
+.toc ul a.toc-active {
+    color: var(--accent-primary);
+    font-weight: 400;
+}
+
+/* ── Public TOC (details/summary block) ─────────────────────────────────── */
+.toc {
+    border: none;
+    border-radius: 0;
+    background: transparent;
+    overflow: visible;
+}
+
+.toc[open] {
+    padding-bottom: 0;
+}
+
+.toc > :not(summary) {
+    padding-left: 0;
+    padding-right: 0;
+}
+
+.toc summary {
+    font-family: var(--font-display);
+    font-size: var(--step-1);
+    font-weight: 400;
+    color: var(--text-primary);
+    padding: 0 0 var(--space-2xs) 0;
+    border-bottom: 1px solid var(--text-primary);
+    display: flex;
+    align-items: center;
+    gap: var(--space-2xs);
+    background: transparent;
+    cursor: pointer;
+    list-style: none;
+}
+
+.toc summary::-webkit-details-marker {
+    display: none;
+}
+
+.toc summary:hover {
+    color: inherit;
+    background: transparent;
+}
+
+/* Caret icon inside summary — visible only on mobile */
+.toc-caret {
+    flex-shrink: 0;
+    transition: transform 0.2s ease;
+}
+
+.toc[open] > summary .toc-caret {
+    transform: rotate(180deg);
+}
+
+/* Sidebar links (about page — custom links below TOC) */
+.toc-sidebar-link:first-of-type {
+    padding-top: var(--space-s);
+    border-top: 1px solid var(--border-primary);
+}
+
+.toc-sidebar-link + .toc-sidebar-link {
+    padding-top: var(--space-xs);
+}
+
+.toc-sidebar-link a {
+    font-size: var(--step--2);
+    color: var(--accent-primary);
+    text-decoration: none;
+    transition: opacity 0.15s;
+}
+
+.toc-sidebar-link a:hover {
+    opacity: 0.8;
+}
+
+/* ── Desktop: sticky sidebar ───────────────────────────────────────────── */
+@media (min-width: 768px) {
+    .toc {
+        position: sticky;
+        top: var(--space-l);
+        grid-column: 1;
+    }
+
+    .toc summary {
+        pointer-events: none;
+    }
+
+    .toc-caret {
+        display: none;
+    }
+}
+
+/* ── Mobile: collapsible TOC ────────────────────────────────────────────── */
+@media (max-width: 767px) {
+    .toc {
+        position: static;
+        grid-column: 1;
+    }
+
+    .toc summary {
+        cursor: pointer;
+        list-style: revert;
+    }
+}