feat(dashboard,diagnostic,elective): add widgets, layout, parent dashboard, role-config, services, elective components

dashboard:

- Add comparison-badge, dashboard-notification-widget, dashboard-responsive-layout, dashboard-time-range-filter

- Add parent-dashboard components directory

- Add config, hooks, and services directories

diagnostic:

- Add role-config and services directory

elective:

- Add elective-course-detail, elective-stats-cards, parent-selection-view components

- Add data-access-settings and data-access-stats

src/modules/elective/data-access-stats.ts

@@ -0,0 +1,88 @@
+import "server-only"
+
+import { cache } from "react"
+import { count, eq, sql } from "drizzle-orm"
+
+import { db } from "@/shared/db"
+import { courseSelections, electiveCourses } from "@/shared/db/schema"
+
+/**
+ * 选课模块管理员概览统计（P1-13 新增）。
+ * 用于 admin/teacher 列表页顶部展示关键指标。
+ */
+
+export interface ElectiveOverviewStats {
+  /** 课程总数 */
+  totalCourses: number
+  /** 总选课人数（已录取 + 候补 + 已选） */
+  totalEnrolled: number
+  /** 平均容量使用率（百分比，0-100） */
+  avgUtilization: number
+  /** 待抽签的课程数（selectionMode=lottery 且 status=open 且存在 selected 记录） */
+  pendingLottery: number
+}
+
+/**
+ * 获取选修课全局概览统计（admin 视角）。
+ *
+ * 实现要点：
+ * - 4 个独立查询合并为 3 个 SQL（pendingLottery 需 join），避免 N+1
+ * - 使用 SQL 聚合而非拉全表后 reduce，避免大数据量内存峰值
+ * - admin 不做 scope 过滤（统计全部课程）
+ */
+export const getElectiveOverviewStats = cache(
+  async (): Promise<ElectiveOverviewStats> => {
+    // 并行执行聚合查询
+    const [totalRow, enrolledRow, utilizationRow, pendingRow] = await Promise.all([
+      // 1. 课程总数
+      db
+        .select({ total: count() })
+        .from(electiveCourses),
+
+      // 2. 总选课人数（活跃选课记录数）
+      db
+        .select({ total: count() })
+        .from(courseSelections)
+        .where(
+          sql`${courseSelections.status} IN ('selected', 'enrolled', 'waitlist')`
+        ),
+
+      // 3. 平均容量使用率（capacity > 0 时计算 enrolledCount/capacity 平均值）
+      db
+        .select({
+          avg: sql<number>`COALESCE(
+            AVG(
+              CASE
+                WHEN ${electiveCourses.capacity} > 0
+                THEN ${electiveCourses.enrolledCount}::float / ${electiveCourses.capacity}
+                ELSE 0
+              END
+            ) * 100,
+            0
+          )`,
+        })
+        .from(electiveCourses),
+
+      // 4. 待抽签课程数：lottery 模式且 status=open 且有 selected 状态的选课记录
+      db
+        .select({ total: sql<number>`count(distinct ${electiveCourses.id})` })
+        .from(electiveCourses)
+        .innerJoin(
+          courseSelections,
+          eq(courseSelections.courseId, electiveCourses.id)
+        )
+        .where(
+          sql`${electiveCourses.selectionMode} = 'lottery'
+            AND ${electiveCourses.status} = 'open'
+            AND ${courseSelections.status} = 'selected'`
+        ),
+    ])
+
+    return {
+      totalCourses: totalRow[0]?.total ?? 0,
+      totalEnrolled: enrolledRow[0]?.total ?? 0,
+      avgUtilization: Math.round(Number(utilizationRow[0]?.avg ?? 0)),
+      pendingLottery: pendingRow[0]?.total ?? 0,
+    }
+  }
+)