Add VaultEntry.snippet field (first ~160 chars of content, markdown-stripped).
Implement scan_vault_cached() with git-based incremental caching:
- Writes .laputa-cache.json to vault dir
- On same HEAD: returns cached entries + uncommitted new files
- On different HEAD: re-parses only changed files via git diff
- Falls back to full scan when git unavailable or cache corrupt
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
a5a152ff25