Fix session sidebar scrollbar - make it visible and functional

- Add CSS for .chat-history-list (was missing, only had .chat-sessions-list)
- Add custom scrollbar styling for better UX
- Add min-height: 0 to fix flexbox overflow issue
- Update cache buster (v1769092045) to force CSS reload

Fixes issue where long session lists had no scrollbar, making bottom
sessions inaccessible.

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

public/claude-ide/index.html

@@ -291,7 +291,7 @@
     </script>
 
     <link rel="stylesheet" href="/claude/css/style.css?v=1769027229">
-    <link rel="stylesheet" href="/claude/claude-ide/ide.css?v=1769027229">
+    <link rel="stylesheet" href="/claude/claude-ide/ide.css?v=1769092045">
     <link rel="stylesheet" href="/claude/claude-ide/tag-renderer.css?v=1769027229">
     <link rel="stylesheet" href="/claude/claude-ide/preview-manager.css?v=1769027229">
     <link rel="stylesheet" href="/claude/claude-ide/chat-enhanced.css?v=1769027229">