Adds color field assigned from an 8-colour palette keyed on the user's UUID
hash (Math.abs(id.hashCode()) % 8). Fires via @PrePersist/@PreUpdate/@PostLoad
so both new and existing users get the correct colour at runtime.
V47 migration adds the column and fixes the V46 REVOKE bug that hardcoded
role name 'app_user' instead of CURRENT_USER.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>