feat: 🗓️ 新增任务块排期能力并完善课程与日程模型

Version: 0.1.1.dev.260207

- 新增并测试通过将任务块排进日程接口 ✅
- 批量导入课程接口增加单双周功能，支持只在单双周上课的课程 📚
- 任务块时间定位逻辑调整为「第几周-周几」模式 🧭

refactor: 🔨 重构时间与日程数据结构

- 完成绝对日期与相对时间的转换逻辑 🔄
  - 后续可根据需求灵活决定时间的传入与输出类型
- 再次重构 schedule 表单结构
  - 拆分为 schedule_event（单）与 schedule（多）
  - 建立前者对后者的一对多关系 🧩

fix: 🐛 大幅调整表结构与业务逻辑，修复大量历史遗留 bug 🔥

backend/dao/schedule.go

@@ -0,0 +1,135 @@
+package dao
+
+import (
+	"context"
+	"errors"
+
+	"github.com/LoveLosita/smartflow/backend/model"
+	"github.com/LoveLosita/smartflow/backend/respond"
+	"gorm.io/gorm"
+)
+
+type ScheduleDAO struct {
+	db *gorm.DB
+}
+
+// NewScheduleDAO 创建TaskClassDAO实例
+func NewScheduleDAO(db *gorm.DB) *ScheduleDAO {
+	return &ScheduleDAO{
+		db: db,
+	}
+}
+
+func (dao *ScheduleDAO) AddSchedules(schedules []model.Schedule) ([]int, error) {
+	if err := dao.db.Create(&schedules).Error; err != nil {
+		return nil, err
+	}
+	ids := make([]int, len(schedules))
+	for i, s := range schedules {
+		ids[i] = s.ID
+	}
+	return ids, nil
+}
+
+func (dao *ScheduleDAO) EmbedTaskIntoSchedule(startSection, endSection, dayOfWeek, week, userID, taskID int) error {
+	// 仅更新指定：用户/周/星期/节次区间 的记录，将 embedded_task_id 精准写入 taskID
+	res := dao.db.
+		Table("schedules").
+		Where("user_id = ? AND week = ? AND day_of_week = ? AND section BETWEEN ? AND ?", userID, week, dayOfWeek, startSection, endSection).
+		Update("embedded_task_id", taskID)
+
+	return res.Error
+}
+
+func (dao *ScheduleDAO) GetCourseUserIDByID(ctx context.Context, courseScheduleEventID int) (int, error) {
+	type row struct {
+		UserID *int `gorm:"column:user_id"`
+	}
+
+	var r row
+	err := dao.db.WithContext(ctx).
+		Table("schedule_events").
+		Select("user_id").
+		Where("id = ?", courseScheduleEventID).
+		First(&r).Error
+	if err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return 0, respond.WrongCourseID
+		}
+		return 0, err
+	}
+	if r.UserID == nil {
+		return 0, respond.WrongCourseID
+	}
+	return *r.UserID, nil
+}
+
+// IsCourseEmbeddedByOtherTaskBlock 判断课程在给定节次区间内是否已被其他任务块嵌入（用于业务限制）
+func (dao *ScheduleDAO) IsCourseEmbeddedByOtherTaskBlock(ctx context.Context, courseID, startSection, endSection int) (bool, error) {
+	// 若区间非法，视为不冲突
+	if startSection <= 0 || endSection <= 0 || startSection > endSection {
+		return false, nil
+	}
+
+	var cnt int64
+	err := dao.db.WithContext(ctx).
+		Table("schedules").
+		Where("id = ?", courseID).
+		Where("section BETWEEN ? AND ?", startSection, endSection).
+		Where("embedded_task_id IS NOT NULL AND embedded_task_id <> 0").
+		Count(&cnt).Error
+	if err != nil {
+		return false, err
+	}
+	return cnt > 0, nil
+}
+
+func (dao *ScheduleDAO) HasUserScheduleConflict(ctx context.Context, userID, week, dayOfWeek int, sections []int) (bool, error) {
+	// 无节次则视为无冲突
+	if len(sections) == 0 {
+		return false, nil
+	}
+	// 统计同一用户、同一周、同一天、且节次有交集的排程数量
+	// 约定表字段：user_id, week, day_of_week, section
+	var cnt int64
+	err := dao.db.WithContext(ctx).
+		Table("schedules").
+		Where("user_id = ? AND week = ? AND day_of_week = ?", userID, week, dayOfWeek).
+		Where("section IN ?", sections).
+		Count(&cnt).Error
+	if err != nil {
+		return false, err
+	}
+	return cnt > 0, nil
+}
+
+func (dao *ScheduleDAO) IsCourseTimeMatch(ctx context.Context, courseScheduleEventID, week, dayOfWeek, startSection, endSection int) (bool, error) {
+	// 区间非法直接不匹配
+	if startSection <= 0 || endSection <= 0 || startSection > endSection {
+		return false, nil
+	}
+
+	// 核对该课程事件在指定 周\+星期 下，是否存在覆盖整个节次区间的排程记录
+	// 说明：此处按你当前表结构的用法（schedule\_events 存事件，schedules 存节次明细）来写：
+	// schedules 里通过 schedule\_event\_id 关联到 schedule\_events.id
+	var cnt int64
+	err := dao.db.WithContext(ctx).
+		Table("schedules").
+		Where("event_id = ?", courseScheduleEventID).
+		Where("week = ? AND day_of_week = ?", week, dayOfWeek).
+		Where("section BETWEEN ? AND ?", startSection, endSection).
+		Count(&cnt).Error
+	if err != nil {
+		return false, err
+	}
+
+	// 需要区间内的每一节都存在记录才算匹配
+	return cnt == int64(endSection-startSection+1), nil
+}
+
+func (dao *ScheduleDAO) AddScheduleEvent(scheduleEvent *model.ScheduleEvent) (int, error) {
+	if err := dao.db.Create(&scheduleEvent).Error; err != nil {
+		return 0, err
+	}
+	return scheduleEvent.ID, nil
+}