Add CreateTombstone() to MemoryStorage and deleteBatchFallback() to handle deletion when SQLite is not available. This fixes the error "tombstone operation not supported by this storage backend" when using bd delete with --no-db flag. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>