feat(user-mgmt): register new users with specific roles

[gery25]

📝 Description (User Story)

As a Technical Director,
I want to register new users by assigning them a specific role
so that I can delegate responsibilities in a controlled manner and ensure each collaborator has access only to the functions required for their job.

🔗 Parent Epic

Part of: #129

✅ Acceptance Criteria (Fit Criteria)

• A new user is created with a specific role.
• The system must confirm that credentials have been sent by email.
• The new user must be able to access only the permitted tools.

🛠️ Technical Checkpoints

• Implement the registration form in the User Management panel.
• Create backend logic for user creation and role assignment.
• Integrate with an email service to send welcome credentials.
• Implement role-based access control (RBAC) for the created user.