Admin: Update User Role

[ayshadogo]

Description:
Allow admins to change a user's role.

Tasks:

• Create PATCH /api/admin/users/:id/role
• Require admin role
• Accept role field: user | admin
• Prevent an admin from downgrading their own role
• Return updated user

Acceptance Criteria:
Admin can promote/demote users; self-demotion is blocked.

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[Anichris-koded]

Hello! I’d love to take on this issue. I’ve reviewed the requirements and have a clear path forward for the implementation. I estimate I can have a PR ready within about 3 hours of being assigned. Could you please assign this to me?