- Add starbook_slots table (new, separate from booth_slots)
- Change total_slots from hardcoded 15 to dynamic fan_profiles.starbook_limit
- Clarify same asset_id cannot be registered as multiple types
- Add placed_at to SlotAsset proto and TypeScript
- Fix grade=0 vs NULL explanation in DB/API contract
- Update affected scope (4 new tables, new StarbookSlotRepository)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
