Summary

This PR consolidates YAML parsing by replacing js-yaml with yaml (eemeli's library) across the codebase.

Motivation

• We were maintaining two YAML libraries (js-yaml and yaml) with overlapping functionality
• The yaml library is already used in core frontmatter parsing and provides richer features (better TypeScript support, parseDocument API for enhanced error handling, comment/anchor support)
• Reduces bundle size and dependency surface area
• Improves maintainability by having a single YAML implementation

Test plan

• All existing tests pass

Checklist

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