feat(teacher-bff): 添加考试作业成绩聚合端点

env.ts 新增 CoreEduServiceUrl
teacher.service 新增 listExamsByClass/listHomeworkByClass/listGradesByExam 三个聚合方法
teacher.controller 暴露 3 个 GET 端点:
  /teacher/classes/:classId/exams
  /teacher/classes/:classId/homework
  /teacher/exams/:examId/grades

验证: 3 端点全部 200 返回 core-edu 数据

services/teacher-bff/src/teacher/teacher.service.ts

@@ -49,4 +49,43 @@ export class TeacherService {
     };
     return json.data ?? [];
   }
+
+  // 聚合班级下的考试列表（core-edu）
+  async listExamsByClass(classId: string): Promise<unknown> {
+    const res = await fetch(
+      `${env.CoreEduServiceUrl}/exams/class/${encodeURIComponent(classId)}`,
+      { headers: { "x-user-id": "bff" } },
+    );
+    if (!res.ok) {
+      return [];
+    }
+    const json = (await res.json()) as { success: boolean; data?: unknown };
+    return json.data ?? [];
+  }
+
+  // 聚合班级下的作业列表（core-edu）
+  async listHomeworkByClass(classId: string): Promise<unknown> {
+    const res = await fetch(
+      `${env.CoreEduServiceUrl}/homework/class/${encodeURIComponent(classId)}`,
+      { headers: { "x-user-id": "bff" } },
+    );
+    if (!res.ok) {
+      return [];
+    }
+    const json = (await res.json()) as { success: boolean; data?: unknown };
+    return json.data ?? [];
+  }
+
+  // 聚合考试下的成绩列表（core-edu）
+  async listGradesByExam(examId: string): Promise<unknown> {
+    const res = await fetch(
+      `${env.CoreEduServiceUrl}/grades/exam/${encodeURIComponent(examId)}`,
+      { headers: { "x-user-id": "bff" } },
+    );
+    if (!res.ok) {
+      return [];
+    }
+    const json = (await res.json()) as { success: boolean; data?: unknown };
+    return json.data ?? [];
+  }
 }