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/router/router.go

@@ -28,6 +28,7 @@ type RouterDeps struct {
 	ScheduleHandler          *handler.ScheduleHandler
 	GradeHandler             *handler.GradeHandler
 	ExamHandler              *handler.ExamHandler
+		EmptyClassroomHandler    *handler.EmptyClassroomHandler
 	RoleHandler              *handler.RoleHandler
 	AdminUserHandler         *handler.AdminUserHandler
 	AdminPostHandler         *handler.AdminPostHandler
@@ -71,6 +72,7 @@ type Router struct {
 	scheduleHandler          *handler.ScheduleHandler
 	gradeHandler             *handler.GradeHandler
 	examHandler              *handler.ExamHandler
+	emptyClassroomHandler    *handler.EmptyClassroomHandler
 	roleHandler              *handler.RoleHandler
 	adminUserHandler         *handler.AdminUserHandler
 	adminPostHandler         *handler.AdminPostHandler
@@ -117,6 +119,7 @@ func New(deps RouterDeps) *Router {
 		scheduleHandler:          deps.ScheduleHandler,
 		gradeHandler:             deps.GradeHandler,
 		examHandler:              deps.ExamHandler,
+		emptyClassroomHandler:    deps.EmptyClassroomHandler,
 		roleHandler:              deps.RoleHandler,
 		adminUserHandler:         deps.AdminUserHandler,
 		adminPostHandler:         deps.AdminPostHandler,
@@ -372,6 +375,16 @@ func (r *Router) setupRoutes() {
 			}
 		}
 
+		// 空教室路由
+		if r.emptyClassroomHandler != nil {
+			classrooms := v1.Group("/classrooms")
+			classrooms.Use(authMiddleware)
+			{
+				classrooms.GET("", r.emptyClassroomHandler.ListEmptyClassrooms)
+				classrooms.POST("/sync", r.emptyClassroomHandler.SyncEmptyClassrooms)
+			}
+		}
+
 		// 学习资料路由（公开）
 		if r.materialHandler != nil {
 			materials := v1.Group("/materials")