[BE-59] Add unit tests for UsersService

[mftee]

Overview

UsersService has no tests. The service is a dependency of AuthService and UsersController, so bugs here propagate widely.

Test Cases to Cover

• create() — creates and returns user record
• findById() — returns user when found, returns null when not found
• findByEmail() — returns user when found, returns null when not found
• update() — applies partial updates and returns updated entity
• softDelete() — sets deletedAt without removing the row

File

src/users/users.service.spec.ts