Fix sidebar: flatten wrapper nodes before grouping, copy sidebar.json to _site

The sidebar JS now flattens single-child wrapper nodes (e.g. "OCaml package
documentation" > "reference") before applying package grouping, so it works
correctly with both 2-level and 3-level sidebar structures. Also copies
sidebar.json to _site/ in the deploy script, and removes unused
groupSidebarData function.

Co-Authored-By: Claude Opus 4.6 <[e-mail]>

deploy-site.sh

···
 cp -rf "$DUNE_DOC/reference/"* "$SITE/reference/"
 mkdir -p "$SITE/odoc.support/"
 cp -rf "$DUNE_DOC/odoc.support/"* "$SITE/odoc.support/"
+# sidebar.json is fetched at runtime by the sidebar JS
+cp -f "$DUNE_DOC/sidebar.json" "$SITE/sidebar.json"
 echo "  assembled into $SITE/"
 
 echo ""

odoc-jons-plugins/src/odoc_jons_plugins_js.ml

···
   return result.concat(ungrouped);
 }
 
-// Apply grouping to the sidebar data tree.
-// The structure is: [root] -> [reference] -> [packages...]
-// We group the packages level.
-function groupSidebarData(data) {
-  return data.map(function(entry) {
-    var children = entry.children || [];
-    return {
-      node: entry.node,
-      children: groupPackages(children)
-    };
-  });
-}
-
 // Sidebar rendering
 function renderEntry(entry) {
   var node = entry.node;
···
 function initSidebar(data) {
   var container = document.getElementById('sidebar-content');
   if (!container) return;
-  var grouped = groupSidebarData(data);
-  // Flatten the top-level wrapper (e.g. "OCaml package documentation")
-  // since everything lives under it — render its children directly.
-  var entries = grouped.length === 1 ? grouped[0].children : grouped;
+  // Flatten single-child wrapper nodes (e.g. "OCaml package documentation" >
+  // "reference") — they add nesting without value.
+  var entries = data;
+  while (entries.length === 1 && entries[0].children && entries[0].children.length > 0) {
+    entries = entries[0].children;
+  }
+  // Group the packages into sections
+  entries = groupPackages(entries);
   var html = '<ul>' + entries.map(renderEntry).join('') + '</ul>';
   container.innerHTML = html;