refactor(layout): consolidate backend codebase into backend/ package and clean root directory

- Moved cmd/, core/, plugins/, pkg/, downstream/, and main.go into backend/ directory
- Batch updated all Go source files to import github.com/Rain-kl/Wavelet/backend/...
- Updated Makefile, scripts/swagger.sh, architecture guards, and platform skills
- Passed all quality gates (100% tests, 0 lint issues, clean build)

backend/plugins/drivers/driver_asynq_cron/schedule.go

@@ -0,0 +1,37 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package driver_asynq_cron
+
+import (
+	"context"
+	"time"
+
+	db "github.com/Rain-kl/Wavelet/backend/plugins/infra/database"
+)
+
+// Schedule 定时任务配置表
+type Schedule struct {
+	ID        uint64    `json:"id,string" gorm:"primaryKey"`
+	Name      string    `json:"name" gorm:"size:128;not null"`
+	TaskType  string    `json:"task_type" gorm:"size:64;not null"`
+	Cron      string    `json:"cron" gorm:"size:64;not null"`
+	Payload   string    `json:"payload" gorm:"type:text"`
+	IsActive  bool      `json:"is_active" gorm:"not null;default:true"`
+	CreatedAt time.Time `json:"created_at" gorm:"autoCreateTime;index"`
+	UpdatedAt time.Time `json:"updated_at" gorm:"autoUpdateTime"`
+}
+
+// TableName 表名
+func (Schedule) TableName() string {
+	return "w_schedules"
+}
+
+// ListActiveSchedules 查询所有已启用的定时任务配置
+func ListActiveSchedules(ctx context.Context) ([]Schedule, error) {
+	var schedules []Schedule
+	if err := db.DB(ctx).Where("is_active = ?", true).Find(&schedules).Error; err != nil {
+		return nil, err
+	}
+	return schedules, nil
+}