Missing User Management and Role Assignment UI #14

Problem:
While the system supports Role-Based Access Control (RBAC) via AdminSeeder, there is no interface for administrators
to manage users or assign roles. All role management must currently be performed manually via direct database
manipulation.

Current State:

• Roles exist in the DB but are inaccessible via UI.
• Admin cannot see a list of registered users.
• Admin cannot promote/demote users to different roles (e.g., from User to Admin).

Suggested Improvement:
Create a "Users" section within the Admin area that allows:

1. User List: View all registered users (Email, Username, Current Role).
2. Role Management: A simple dropdown or toggle to change a user's role.

Security Requirement:
The new /Admin/Users route must be strictly protected with [Authorize(Roles = "Admin")].