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/users.e2e-spec.ts

@@ -155,4 +155,74 @@ describe('Users (e2e)', () => {
       .send({ ids: [id] })
       .expect(200);
   });
+
+  it('creates and updates a linked employee from the user payload', async () => {
+    const suffix = Date.now().toString().slice(-6);
+    const employee = await request(app.getHttpServer())
+      .post('/employees')
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({
+        code: `UE_${suffix}`,
+        name: 'Ada Lovelace',
+        phone: '+6281234567890',
+        position: 'sales',
+      })
+      .expect(201);
+    const employeeId = (employee.body as { id: string }).id;
+
+    const created = await request(app.getHttpServer())
+      .post('/users')
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({
+        username: `usr_emp_${suffix}`,
+        password: 'password123',
+        employeeId,
+      })
+      .expect(201);
+
+    expect(created.body.employee).toMatchObject({
+      id: employeeId,
+      code: `UE_${suffix}`,
+      name: 'Ada Lovelace',
+    });
+    const userId = (created.body as { id: string }).id;
+
+    const linked = await request(app.getHttpServer())
+      .get(`/employees/${employeeId}`)
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .expect(200);
+    expect(linked.body.user).toMatchObject({
+      id: userId,
+      username: `usr_emp_${suffix}`,
+    });
+
+    const existing = await request(app.getHttpServer())
+      .post('/employees')
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({
+        code: `UL_${suffix}`,
+        name: 'Grace Hopper',
+        phone: '+6281234567891',
+        position: 'crew',
+      })
+      .expect(201);
+    const existingId = (existing.body as { id: string }).id;
+
+    const reassigned = await request(app.getHttpServer())
+      .patch(`/users/${userId}`)
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({ employeeId: existingId })
+      .expect(200);
+    expect(reassigned.body.employee).toMatchObject({
+      id: existingId,
+      name: 'Grace Hopper',
+    });
+
+    const unlinked = await request(app.getHttpServer())
+      .patch(`/users/${userId}`)
+      .set('Authorization', `Bearer ${adminAccessToken}`)
+      .send({ employeeId: null })
+      .expect(200);
+    expect(unlinked.body.employee).toBeNull();
+  });
 });