toc: add independent scrollbar for desktop TOC sidebar

- Added max-height, overflow-y: auto, overscroll-behavior: contain,
  and scrollbar-width: thin to .toc in the desktop media query (toc.css)
- This gives the TOC its own scrollbar when its content exceeds the
  viewport height, scrolling independently from the main content
- Affects both public pages (about, charte, licence via .page-content)
  and admin pages (acces, parametres, contenus via .admin-main--toc)

TODO.md

@@ -1,2 +1,3 @@
 - [x] Fix markdown cheatsheet modal 500 error — missing `require_once bootstrap.php` in `app/public/admin/markdown-cheatsheet-fragment.php`
 - [x] Add `padding-bottom` to `.md-cheatsheet-dialog` so last table row isn't flush against dialog edge
+- [x] Add independent scrollbar for TOC in charte/licence/apropos + admin pages (max-height + overflow-y: auto on .toc desktop)

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

@@ -110,12 +110,16 @@
     opacity: 0.8;
 }
 
-/* ── Desktop: sticky sidebar ───────────────────────────────────────────── */
+/* ── Desktop: sticky sidebar with independent scroll ──────────────────── */
 @media (min-width: 768px) {
     .toc {
         position: sticky;
         top: var(--space-l);
         grid-column: 1;
+        max-height: calc(100vh - var(--space-xl) - var(--space-2xl));
+        overflow-y: auto;
+        overscroll-behavior: contain;
+        scrollbar-width: thin;
     }
 
     .toc summary {