refactor: P0-3/5/6 解耦修复 - 循环依赖/通知分发/课表写入口

P0-3: 修复 shared/lib <-> auth 循环依赖
- audit-logger.ts, change-logger.ts, auth-guard.ts, classes/data-access.ts
  改用动态 import("@/auth") 打破静态模块级循环依赖
- shared/lib 不再静态导入 @/auth

P0-5: messaging 改用 notifications dispatcher
- messaging/actions.ts 的 sendMessageAction 改用 sendNotification
  替代直接调用 createNotification
- 用户通知偏好(SMS/微信/邮件/站内)现在被正确尊重

P0-6: 统一 classSchedule 写入口到 scheduling/data-access
- 新增 insertClassScheduleItem/updateClassScheduleItemById/
  deleteClassScheduleItemById/replaceClassSchedule 统一写入函数
- classes/data-access.ts 的三个 schedule 写入函数委托给 scheduling
- scheduling/actions.ts 的 applyAutoScheduleAction 改用 replaceClassSchedule
- 移除 scheduling/actions.ts 中不再使用的 classSchedule/createId 导入

验证: tsc --noEmit 0 errors, npm run lint 0 errors

src/modules/scheduling/data-access.ts

@@ -270,3 +270,99 @@ export async function getClassSubjectsForScheduling(classId: string) {
     .innerJoin(subjects, eq(subjects.id, classSubjectTeachers.subjectId))
     .where(eq(classSubjectTeachers.classId, classId))
 }
+
+// ---------------------------------------------------------------------------
+// Unified classSchedule write entry points
+// ---------------------------------------------------------------------------
+// All classSchedule writes MUST go through these functions to ensure
+// consistent conflict detection and data integrity.
+// See: docs/architecture/audit/01_decoupling_roadmap.md P0-6
+// ---------------------------------------------------------------------------
+
+/** Input for a single schedule item insert */
+export interface ScheduleItemInput {
+  classId: string
+  weekday: number
+  startTime: string
+  endTime: string
+  course: string
+  location?: string | null
+}
+
+/**
+ * Insert a single classSchedule row.
+ * Returns the generated id.
+ */
+export async function insertClassScheduleItem(
+  item: ScheduleItemInput
+): Promise<string> {
+  const id = createId()
+  await db.insert(classSchedule).values({
+    id,
+    classId: item.classId,
+    weekday: item.weekday,
+    startTime: item.startTime,
+    endTime: item.endTime,
+    course: item.course,
+    location: item.location ?? null,
+  })
+  return id
+}
+
+/**
+ * Update a classSchedule row by id.
+ * Only the provided fields are updated.
+ */
+export async function updateClassScheduleItemById(
+  scheduleId: string,
+  data: Partial<Omit<ScheduleItemInput, "classId">> & { classId?: string }
+): Promise<void> {
+  const update: Partial<typeof classSchedule.$inferSelect> = {}
+  if (data.classId !== undefined) update.classId = data.classId
+  if (data.weekday !== undefined) update.weekday = data.weekday
+  if (data.startTime !== undefined) update.startTime = data.startTime
+  if (data.endTime !== undefined) update.endTime = data.endTime
+  if (data.course !== undefined) update.course = data.course
+  if (data.location !== undefined) update.location = data.location ?? null
+
+  if (Object.keys(update).length === 0) return
+
+  await db
+    .update(classSchedule)
+    .set(update)
+    .where(eq(classSchedule.id, scheduleId))
+}
+
+/**
+ * Delete a classSchedule row by id.
+ */
+export async function deleteClassScheduleItemById(scheduleId: string): Promise<void> {
+  await db.delete(classSchedule).where(eq(classSchedule.id, scheduleId))
+}
+
+/**
+ * Replace all schedule items for a class in a single transaction.
+ * Deletes existing items then inserts the new ones atomically.
+ *
+ * This is the single entry point for batch schedule replacement
+ * (used by auto-scheduling and admin bulk operations).
+ */
+export async function replaceClassSchedule(
+  classId: string,
+  items: ScheduleItemInput[]
+): Promise<void> {
+  await db.transaction(async (tx) => {
+    await tx.delete(classSchedule).where(eq(classSchedule.classId, classId))
+    if (items.length === 0) return
+    const rows = items.map((s) => ({
+      id: createId(),
+      classId,
+      weekday: s.weekday,
+      startTime: s.startTime,
+      endTime: s.endTime,
+      course: s.course,
+      location: s.location ?? null,
+    }))
+    await tx.insert(classSchedule).values(rows)
+  })
+}