Implement Nieuwe permissie role 'verantwoordelijke'

De nieuwe permissie role 'verantwoordelijk' is nodig om items in te boeken en verdere beheers functies die betrekking hebben tot de inventaris

No files or tests are named in the issue, so first inspect where user roles are defined and checked. Start with the authorization/rbac code and user-role models, then trace the inventory flows for booking and management actions to wire in `verantwoordelijke`. Update role storage (migration/seed/config) if needed, then run permission-related tests or manual inventory actions. Done means the new role is persisted and can perform the intended inventory tasks without breaking existing permissions.

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