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/empty_classroom.go

@@ -0,0 +1,26 @@
+package model
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+type EmptyClassroom struct {
+	ID        string `json:"id" gorm:"type:varchar(36);primaryKey"`
+	UserID    string `json:"user_id" gorm:"type:varchar(36);index;not null"`
+	Semester  string `json:"semester" gorm:"type:varchar(30);not null"`
+	Classroom string `json:"classroom" gorm:"type:varchar(60);not null"`
+	Weekday   string `json:"weekday" gorm:"type:varchar(100)"`
+	Periods   string `json:"periods" gorm:"type:text"`
+	Weeks     string `json:"weeks" gorm:"type:varchar(30)"`
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
+func (e *EmptyClassroom) BeforeCreate(tx *gorm.DB) error {
+	SetUUIDIfEmpty(&e.ID)
+	return nil
+}
+
+func (EmptyClassroom) TableName() string { return "empty_classrooms" }

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{},