Fix repertoire column scrolling + admin TOC duplication

- repertoire.css: add min-height: 0 to column <ul> scroll containers so
  grid 1fr row shrinks below content and overflow-y: auto activates
- admin-toc.js: add __adminTocBuilt guard + nav.children check to prevent
  double population when loaded both via admin.min.js and direct <script>
- admin-toc.php: remove duplicate <script src="admin-toc.js"> tag —
  JS is already bundled in admin.min.js

app/templates/admin/partials/admin-toc.php

@@ -8,8 +8,6 @@
 ?>
 <aside id="admin-toc" class="admin-toc" aria-label="Sur cette page">
     <nav class="admin-toc-list" id="admin-toc-list">
-        <!-- populated by JS -->
+        <!-- populated by JS (admin-toc.js, loaded via admin.min.js) -->
     </nav>
 </aside>
-
-<script src="<?= App::assetV('/assets/js/app/admin-toc.js') ?>"></script>