Enhance employee and user management with linked user functionality

- Introduced `EmployeeUserWrite` type to manage user details associated with employees.
- Updated `EmployeesService` and `EmployeesRepository` to support user assignment and retrieval by user ID.
- Enhanced DTOs to include user information for employee creation and updates.
- Implemented validation to ensure proper handling of user data during employee operations.
- Added unit and e2e tests to validate the new functionality and ensure data integrity in user-employee relationships.
- Modified existing controllers to accommodate the new user linkage features in employee management.

test/employees.e2e-spec.ts

@@ -215,4 +215,67 @@ describe('Employees (e2e)', () => {
 
     expect(res.body).toMatchObject({ imported: 1 });
   });
+
+  it('creates and updates a linked user from the employee payload', async () => {
+    const suffix = Date.now().toString().slice(-6);
+    const created = await request(app.getHttpServer())
+      .post('/employees')
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({
+        code: `EU_${suffix}`,
+        name: 'Ada Lovelace',
+        phone: '+6281234567890',
+        position: 'sales',
+        user: {
+          username: `emp_usr_${suffix}`,
+          password: 'password123',
+        },
+      })
+      .expect(201);
+
+    expect(created.body.user).toMatchObject({
+      username: `emp_usr_${suffix}`,
+    });
+    const employeeId = (created.body as { id: string }).id;
+    const linkedUserId = (created.body.user as { id: string }).id;
+
+    const user = await request(app.getHttpServer())
+      .get(`/users/${linkedUserId}`)
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .expect(200);
+    expect(user.body.employee).toMatchObject({
+      id: employeeId,
+      code: `EU_${suffix}`,
+    });
+
+    const renamed = await request(app.getHttpServer())
+      .patch(`/employees/${employeeId}`)
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({ user: { username: `emp_ren_${suffix}` } })
+      .expect(200);
+    expect(renamed.body.user).toMatchObject({
+      id: linkedUserId,
+      username: `emp_ren_${suffix}`,
+    });
+
+    const existingUser = await request(app.getHttpServer())
+      .post('/users')
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({
+        username: `emp_ex_${suffix}`,
+        password: 'password123',
+      })
+      .expect(201);
+    const existingUserId = (existingUser.body as { id: string }).id;
+
+    const assigned = await request(app.getHttpServer())
+      .patch(`/employees/${employeeId}`)
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({ user: { id: existingUserId, username: `emp_as_${suffix}` } })
+      .expect(200);
+    expect(assigned.body.user).toMatchObject({
+      id: existingUserId,
+      username: `emp_as_${suffix}`,
+    });
+  });
 });