Fix folder icon consistency by normalizing directory names

Capitalize and format folder names consistently (e.g., "photography" ->
"Photography") when no index.md exists, ensuring the same icon color
appears in both the browse dropdown and on the directory page itself.

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

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

tuftecms/blueprints/api.py

@@ -264,7 +264,7 @@ def directory_tree():
 
             if item.is_dir():
                 # For folders, try to get title from index.md
-                display_name = item.name
+                display_name = item.name.replace("-", " ").replace("_", " ").title()
                 index_file = item / 'index.md'
                 if index_file.exists():
                     title = get_cached_markdown_title(index_file)