- Remove FK constraint to invoice_items table (not yet created)
- Shorten index names to avoid MariaDB 64-char limit
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Credit notes can exist independently of orders. Foreign keys will be
added when orders and refunds modules are implemented.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>