fix: add support for folder note/index pages

[tylerdave]

No description provided.

[github-actions]

Docs Site preview: https://dea8560b.rockgarden.pages.dev

[claude]

LGTM. The previously flagged logging issue has been addressed — loader.py now uses logging.getLogger(__name__) with logger.warning(...) throughout, matching the pattern in render/engine.py.

The folder-note detection logic is correct: the parts[-1] == parts[-2] slug comparison reliably identifies folder notes across all url_style values, custom slugs bypass the rewrite, and index.md files are not affected. The conflict resolution in load_content correctly demotes folder notes when an explicit index.md exists. The _index_page fallback in store.py is properly gated so stem-based matches always take precedence over the folder-name fallback. Test coverage is solid across all key cases.