* Implement dynamic role assignment for new family creators.
Introduced `User.role_for_new_family_creator` to assign `super_admin` to the first user of an instance and a configurable fallback role (e.g., `admin`) to subsequent users. Updated controllers and tests accordingly.
* Update default fallback role for family creators to admin.
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Co-authored-by: luckyPipewrench <luckypipewrench@proton.me>