feat(content): v2 扩展 Elective/LessonPlan/CoursePlan 三业务域

新增 3 个业务域（10 RPC）：
- ElectiveService: 选修课列表/学生选课记录/选课/退课（含容量与重复校验）
- LessonPlanService: 教师备课列表/学生备课列表（仅 published）/详情
- CoursePlanService: 学生课程计划列表/详情
- KnowledgeGraphService.GetKnowledgePath: 与 GetLearningPath 同实现

新增 4 张 MySQL 表（elective_courses/selections/lesson_plans/course_plans），含完整索引。

新增 11 个权限点，覆盖 admin/teacher/student/parent 四角色。

proto 由 4 Service/22 RPC 扩展至 7 Service/32 RPC，v1 全部 RPC 保持向后兼容。

修复 logger.ts pino 导入: default import 在 NodeNext ESM 下不可调用，
改用 named import（与 iam/msg/core-edu 对齐）。

Docker 本地测试全部通过（HTTP + gRPC 双协议），健康检查、
Elective/LessonPlan/CoursePlan CRUD、4 个新 gRPC Service 全部验证通过。

nextstep-v2.md 已创建，记录上下游依赖与 6 项联调待办。

services/content/src/electives/electives.repository.ts

@@ -0,0 +1,118 @@
+import { eq, and } from "drizzle-orm";
+import { getDb } from "../config/database.js";
+import {
+  electiveCourses,
+  electiveSelections,
+  type ElectiveCourse,
+  type NewElectiveCourse,
+  type ElectiveSelection,
+  type NewElectiveSelection,
+} from "./electives.schema.js";
+
+export class ElectivesRepository {
+  async findCourseById(id: string): Promise<ElectiveCourse | undefined> {
+    const [result] = await getDb()
+      .select()
+      .from(electiveCourses)
+      .where(eq(electiveCourses.id, id))
+      .limit(1);
+    return result;
+  }
+
+  async findCourses(query?: {
+    subjectId?: string;
+    page?: number;
+    pageSize?: number;
+  }): Promise<ElectiveCourse[]> {
+    const db = getDb();
+    let q = db.select().from(electiveCourses).$dynamic();
+    if (query?.subjectId) {
+      q = q.where(eq(electiveCourses.subjectId, query.subjectId));
+    }
+    const pageSize = query?.pageSize ?? 20;
+    const page = query?.page ?? 1;
+    return q.limit(pageSize).offset((page - 1) * pageSize);
+  }
+
+  async createCourse(data: NewElectiveCourse): Promise<void> {
+    await getDb().insert(electiveCourses).values(data);
+  }
+
+  async updateCourse(
+    id: string,
+    data: Partial<NewElectiveCourse>,
+  ): Promise<void> {
+    await getDb()
+      .update(electiveCourses)
+      .set(data)
+      .where(eq(electiveCourses.id, id));
+  }
+
+  async deleteCourse(id: string): Promise<void> {
+    await getDb().delete(electiveCourses).where(eq(electiveCourses.id, id));
+  }
+
+  async findSelectionsByStudent(
+    studentId: string,
+    status?: string,
+  ): Promise<ElectiveSelection[]> {
+    const db = getDb();
+    let q = db
+      .select()
+      .from(electiveSelections)
+      .where(eq(electiveSelections.studentId, studentId))
+      .$dynamic();
+    if (status) {
+      q = q.where(eq(electiveSelections.status, status));
+    }
+    return q;
+  }
+
+  async findActiveSelection(
+    studentId: string,
+    courseId: string,
+  ): Promise<ElectiveSelection | undefined> {
+    const [result] = await getDb()
+      .select()
+      .from(electiveSelections)
+      .where(
+        and(
+          eq(electiveSelections.studentId, studentId),
+          eq(electiveSelections.courseId, courseId),
+          eq(electiveSelections.status, "selected"),
+        ),
+      )
+      .limit(1);
+    return result;
+  }
+
+  async createSelection(data: NewElectiveSelection): Promise<void> {
+    await getDb().insert(electiveSelections).values(data);
+  }
+
+  async updateSelection(
+    id: string,
+    data: Partial<NewElectiveSelection>,
+  ): Promise<void> {
+    await getDb()
+      .update(electiveSelections)
+      .set(data)
+      .where(eq(electiveSelections.id, id));
+  }
+
+  async countEnrolled(courseId: string): Promise<number> {
+    const db = getDb();
+    const rows = await db
+      .select()
+      .from(electiveSelections)
+      .where(
+        and(
+          eq(electiveSelections.courseId, courseId),
+          eq(electiveSelections.status, "selected"),
+        ),
+      );
+    return rows.length;
+  }
+}
+
+export const electivesRepository = new ElectivesRepository();