List all notes in a given category inside /Notes.

Args:
    category_name: The subfolder name inside /Notes

Returns:
    List of note filenames (.md) in that category.

Read a Markdown (.md) file.

Args:
    filename: Name of the note file, e.g., "note1.md"
    category: Optional category folder. If None, read from /Notes root.

Returns:
    Content of the note as a string.

Create a new Markdown (.md) note.

- If category is None → stored in /Notes/<filename>
- If category is provided → stored in /Notes/<category>/<filename>

Rename an existing category inside Notes.

Args:
    old_name: Current name of the category.
    new_name: New name for the category.