IAV-91/refactor: remove BASE_API constant from UserServicePath

This MR simplifies the UserServicePath class by removing the redundant BASE_API constant.

Changes

• Removed BASE_API constant (/api/user)
• Updated base path constants to be directly defined:
  • USER_BASE: now /super_admin (was BASE_API + "/super_admin")
  • ADMIN_BASE: now /admins (was BASE_API + "/admins")
  • COLLABORATOR_BASE: now /collaborators (was BASE_API + "/collaborators")

Closes IAV-91