Function parse_frontmatter 

pub fn parse_frontmatter(raw: &str) -> (Option<SkillFrontmatter>, String)

Parse YAML frontmatter from a markdown document.

Returns the parsed frontmatter (if valid) and the body content with frontmatter delimiters stripped.

Frontmatter format:

---
name: my-skill
description: A useful skill
---
Body content here...