feat(runner): implement empty classroom sync functionality

Add support for fetching and synchronizing empty classroom data. This includes new protobuf definitions for task payloads and results, database models, repository, service, and HTTP handlers.

- Add `TASK_TYPE_GET_EMPTY_CLASSROOM` to `TaskType` enum
- Implement `EmptyClassroom` model and auto-migration
- Add `EmptyClassroomHandler` with `GET` and `POST /sync` routes
- Implement `EmptyClassroomSyncService` and `EmptyClassroomRepository`
- Update dependency injection with wire sets

internal/model/init.go

@@ -193,6 +193,7 @@ func autoMigrate(db *gorm.DB) error {
 		&Grade{},
 		&GpaSummary{},
 		&Exam{},
+			&EmptyClassroom{},
 
 		// 用户活跃相关
 		&UserActiveLog{},