- Add frontmatterHide extension using CM6 StateField for cross-line replacement
- Frontmatter (--- ... ---) collapsed to small "---" indicator when cursor is outside
- Cursor entering the frontmatter block reveals full YAML content
- Editor places cursor after frontmatter on note load so it starts hidden
- Add Playwright test verifying frontmatter is hidden by default
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>