v0.12.23: Fix contact persons not saving

The CustomerContact model introduced in v0.12.22 was accidentally omitted from the AutoMigrate list in database/database.go. As a result the customer_contacts table was never created, and any attempt to add or edit a contact person returned "Failed to save contact".

The model is now registered correctly; the table is created automatically on first boot after upgrading.

Download v0.12.23 from the download page or pull the latest release tag. No other changes — run the new binary in-place and the table will appear on startup.