webhook_events referenced orders and subscriptions tables that don't
exist yet (billing module). Switched to plain unsignedBigInteger columns
with indexes — FKs can be added when the billing tables are created.
Co-Authored-By: Virgil <virgil@lethean.io>
- 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>