Fix sidebar scrolling for smaller viewports

- Added CSS override to enable scrolling in fixed sidebar
- Sidebar now properly scrolls when content exceeds viewport height
- All navigation items and social icons are now accessible on short windows
- Used local override instead of modifying theme directly

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

assets/css/_extra.scss

@@ -4,3 +4,13 @@
     margin-right: 0.2em;
   }
 }
+
+// Fix sidebar scrolling for smaller viewports
+@media (min-width: 940px) {
+  .app-header {
+    height: 100vh !important;
+    overflow-y: auto !important;
+    overflow-x: hidden !important;
+    min-height: unset !important;
+  }
+}