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。

packages/shared-proto/proto/content.proto

@@ -23,6 +23,7 @@ service ChapterService {
 service KnowledgeGraphService {
   rpc GetPrerequisites(GetPrerequisitesRequest) returns (KnowledgePointsResponse);
   rpc GetLearningPath(GetLearningPathRequest) returns (LearningPath);
+  rpc GetKnowledgePath(GetKnowledgePathRequest) returns (LearningPath);
   rpc AddPrerequisite(AddPrerequisiteRequest) returns (Empty);
   rpc RemovePrerequisite(RemovePrerequisiteRequest) returns (Empty);
 }
@@ -38,6 +39,24 @@ service QuestionService {
   rpc SearchQuestions(SearchQuestionsRequest) returns (SearchQuestionsResponse);
 }
 
+service ElectiveService {
+  rpc ListAvailableElectiveCourses(ListAvailableElectiveCoursesRequest) returns (ListElectiveCoursesResponse);
+  rpc ListElectiveSelectionsByStudent(ListElectiveSelectionsByStudentRequest) returns (ListElectiveSelectionsResponse);
+  rpc SelectCourse(SelectCourseRequest) returns (ElectiveSelection);
+  rpc DropCourse(DropCourseRequest) returns (Empty);
+}
+
+service LessonPlanService {
+  rpc ListLessonPlansByTeacher(ListLessonPlansByTeacherRequest) returns (ListLessonPlansResponse);
+  rpc ListLessonPlansByStudent(ListLessonPlansByStudentRequest) returns (ListLessonPlansResponse);
+  rpc GetLessonPlan(GetLessonPlanRequest) returns (LessonPlan);
+}
+
+service CoursePlanService {
+  rpc ListCoursePlansByStudent(ListCoursePlansByStudentRequest) returns (ListCoursePlansResponse);
+  rpc GetCoursePlan(GetCoursePlanRequest) returns (CoursePlan);
+}
+
 message Empty {}
 
 message Textbook {
@@ -272,3 +291,124 @@ message SearchQuestionsResponse {
   int32 total = 2;
   string next_page_token = 3;
 }
+
+// KnowledgeGraphService: GetKnowledgePath (按班级查询学习路径)
+message GetKnowledgePathRequest {
+  string class_id = 1;
+  string subject_id = 2;
+}
+
+// ElectiveService messages
+message ElectiveCourse {
+  string id = 1;
+  string title = 2;
+  string subject_id = 3;
+  string teacher_id = 4;
+  int32 capacity = 5;
+  int32 enrolled_count = 6;
+  string status = 7;
+  string description = 8;
+  int64 created_at = 9;
+  int64 updated_at = 10;
+}
+
+message ElectiveSelection {
+  string id = 1;
+  string student_id = 2;
+  string course_id = 3;
+  string status = 4;
+  int64 selected_at = 5;
+  int64 dropped_at = 6;
+}
+
+message ListAvailableElectiveCoursesRequest {
+  string subject_id = 1;
+  int32 page_size = 2;
+  string page_token = 3;
+}
+
+message ListElectiveCoursesResponse {
+  repeated ElectiveCourse courses = 1;
+  string next_page_token = 2;
+}
+
+message ListElectiveSelectionsByStudentRequest {
+  string student_id = 1;
+  string status = 2;
+}
+
+message ListElectiveSelectionsResponse {
+  repeated ElectiveSelection selections = 1;
+}
+
+message SelectCourseRequest {
+  string student_id = 1;
+  string course_id = 2;
+}
+
+message DropCourseRequest {
+  string student_id = 1;
+  string course_id = 2;
+}
+
+// LessonPlanService messages
+message LessonPlan {
+  string id = 1;
+  string teacher_id = 2;
+  string class_id = 3;
+  string subject_id = 4;
+  string title = 5;
+  string content = 6;
+  string status = 7;
+  google.protobuf.Struct metadata = 8;
+  int64 created_at = 9;
+  int64 updated_at = 10;
+}
+
+message ListLessonPlansByTeacherRequest {
+  string teacher_id = 1;
+  string class_id = 2;
+  string subject_id = 3;
+}
+
+message ListLessonPlansByStudentRequest {
+  string student_id = 1;
+  string class_id = 2;
+}
+
+message ListLessonPlansResponse {
+  repeated LessonPlan lesson_plans = 1;
+}
+
+message GetLessonPlanRequest {
+  string id = 1;
+}
+
+// CoursePlanService messages
+message CoursePlan {
+  string id = 1;
+  string student_id = 2;
+  string class_id = 3;
+  string subject_id = 4;
+  string title = 5;
+  string plan_type = 6;
+  string content = 7;
+  string status = 8;
+  google.protobuf.Struct metadata = 9;
+  int64 created_at = 10;
+  int64 updated_at = 11;
+}
+
+message ListCoursePlansByStudentRequest {
+  string student_id = 1;
+  string class_id = 2;
+  string plan_type = 3;
+}
+
+message ListCoursePlansResponse {
+  repeated CoursePlan course_plans = 1;
+}
+
+message GetCoursePlanRequest {
+  string id = 1;
+}