## ADDED Requirements

### Requirement: scans.fingerprint column
The `scans` table SHALL include a nullable `fingerprint` text column, added idempotently so existing databases migrate cleanly.

#### Scenario: Fresh database
- **WHEN** `db/schema.sql` is applied to an empty database
- **THEN** `scans.fingerprint` exists and is nullable

#### Scenario: Existing database
- **WHEN** `db/schema.sql` is re-applied to a database created before this column
- **THEN** the column is added without error, nullable
