refactor(backend): update employees endpoint and service

- endpoints/employees.py: update employees API endpoint
- services/employee.py: update employee service

server/src/app/api/v1/endpoints/employees.py

@@ -125,3 +125,22 @@ def disable_employee(employee_id: str, db: DbSession) -> EmployeeRead:
         return EmployeeService(db).disable_employee(employee_id)
     except LookupError as exc:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)) from exc
+
+
+@router.post(
+    "/{employee_id}/enable",
+    response_model=EmployeeRead,
+    summary="启用员工",
+    description="将停用员工恢复为在职状态，使其可以重新登录系统。",
+    responses={
+        status.HTTP_404_NOT_FOUND: {
+            "model": ErrorResponse,
+            "description": "员工不存在。",
+        }
+    },
+)
+def enable_employee(employee_id: str, db: DbSession) -> EmployeeRead:
+    try:
+        return EmployeeService(db).enable_employee(employee_id)
+    except LookupError as exc:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail=str(exc)) from exc