Support real subdirectories in wiki instead of escaping / to %2F.
When navigating to a folder, tries README.md, Home.md, index.md
as index pages. If none found, shows a file/folder listing.
Includes:
- Stop escaping / in WebPathFromRequest (wiki_path.go)
- Folder detection with index file fallback
- Auto-generated sidebar folder tree
- Breadcrumb navigation for nested paths
- Folder listing view when no index page exists
- CSS for tree sidebar and folder listing