Detects two classes of vault issues:
1. Stray files in non-protected subfolders (won't be scanned)
2. Filename-title mismatches (filename ≠ slugify(title))
Returns a VaultHealthReport with stray_files and title_mismatches.
Registered as a Tauri command for frontend use.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>