Refactor import statements across multiple modules to use relative paths for better organization and maintainability.

Co-authored-by: Copilot <copilot@github.com>

backend/app/routers/users.py

@@ -1,9 +1,9 @@
 """Users router: self-service profile and admin user management."""
 from fastapi import APIRouter, Depends, HTTPException, status
 
-from backend.app.dependencies import get_current_user, require_admin
-from backend.app.models.users import SetRoleRequest, UpdateUserRequest, UserResponse
-from backend.app.services.users import (
+from ..dependencies import get_current_user, require_admin
+from ..models.users import SetRoleRequest, UpdateUserRequest, UserResponse
+from ..services.users import (
     delete_user,
     get_user,
     list_users,