Tests cover:
- Clone: CustomFieldValue references cloned definitions, not source
- Clone: values are preserved after cloning
- Slots: 404 on non-existent piece, 422 on wrong type, success on correct type
- Conversion: blocked when slots have filled data, allowed when empty
- CustomField: rejects orphan creation, accepts existing field by ID
Also removes legacy JSON structure check (column no longer exists
after normalization) — replaced by slot table checks.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
