admin toc: label rename + padding

- rename 'Sur cette page' to 'Parties'
- add padding-top between PARTIES label and toc links

app/public/assets/css/admin.css

@@ -2240,6 +2240,10 @@ th.admin-ap-col {
 }
 
 /* Admin TOC: same <details class="toc"> as public pages, positioned sticky */
+#admin-toc .toc-list {
+  padding-top: var(--space-2xs);
+}
+
 #admin-toc .toc-list a {
   font-size: var(--step--1);
 }