fix(docs): improve mobile sidebar navigation

The sidebar had all categories expanded by default (collapsed: false),
which on mobile created a 60+ item flat list when opening the sidebar.
Reported by danny on Discord.

Changes:
- Set all top-level categories to collapsed: true (tap to expand)
- Enable autoCollapseCategories: true (accordion — opening one section
  closes others, prevents the overwhelming flat list)
- Enable hideable sidebar (swipe-to-dismiss on mobile)
- Add mobile CSS: larger touch targets (0.75rem padding), bolder
  category headers, visible subcategory indentation with left border,
  wider sidebar (85vw / 360px max), darker backdrop overlay

website/docusaurus.config.ts

@@ -65,6 +65,12 @@ const config: Config = {
       defaultMode: 'dark',
       respectPrefersColorScheme: true,
     },
+    docs: {
+      sidebar: {
+        hideable: true,
+        autoCollapseCategories: true,
+      },
+    },
     navbar: {
       title: 'Hermes Agent',
       logo: {