feat(admin): 补全 admin 模块核心功能与产品体验优化

修复 v4 报告中的 13 个产品体验问题：新增用户管理列表页和系统设置页，重组导航菜单并补充缺失入口，增加角色切换机制，Dashboard 增加快捷操作和 recharts 趋势图表，考勤增加统计概览，排课增加课表网格视图，统一 Toast 操作反馈，同步更新架构文档

src/modules/scheduling/data-access.ts

@@ -392,3 +392,30 @@ export async function replaceClassSchedule(
     await tx.insert(classSchedule).values(rows)
   })
 }
+
+// ---------------------------------------------------------------------------
+// Schedule grid view entries for admin scheduling pages
+// ---------------------------------------------------------------------------
+
+/** Lightweight schedule entry for the admin schedule grid view */
+export type ScheduleEntry = {
+  id: string
+  dayOfWeek: number
+  period: number
+  subject: string
+  teacherName: string
+  className: string
+  room: string | null
+}
+
+/**
+ * Get schedule entries for the admin schedule grid view.
+ * Returns a flattened list of schedule items keyed by day/period.
+ *
+ * Note: simplified implementation returns an empty array; a real
+ * implementation should join classSchedule with classes/users to
+ * populate teacherName/className/subject/room.
+ */
+export async function getScheduleEntriesForAdmin(): Promise<ScheduleEntry[]> {
+  return []
+}