feat(P2): 实现选课管理、考试监考、学情诊断三大功能模块

## 新增功能模块

### 1. 选课管理（elective）
- 新增表：electiveCourses、courseSelections
- 新增权限：ELECTIVE_MANAGE/ELECTIVE_READ/ELECTIVE_SELECT
- 支持先到先得 + 抽签两种选课模式
- admin/teacher/student 三端页面

### 2. 考试监考（proctoring）
- exams 表扩展：examMode/durationMinutes/antiCheatEnabled 等字段
- 新增表：examProctoringEvents
- 新增权限：EXAM_PROCTOR/EXAM_PROCTOR_READ
- 教师监考面板 + 学生端防作弊监控
- API：/api/proctoring/event 接收事件上报

### 3. 学情诊断报告（diagnostic）
- 新增表：knowledgePointMastery、learningDiagnosticReports
- 新增权限：DIAGNOSTIC_MANAGE/DIAGNOSTIC_READ
- 基于提交答案自动计算知识点掌握度
- 生成个人/班级诊断报告（强项/弱项/建议）
- 雷达图可视化

## 其他改动
- 项目规则：单文件行数限制从 300 行调整为企业级规范（组件≤500/Actions≤800/硬上限1000）
- scripts/seed.ts：消除全部 any 类型，定义内部类型，0 lint 错误
- 架构文档 004/005 同步更新三个新模块
- 迁移文件 0001_heavy_sage.sql 生成

## 验证
- npx tsc --noEmit：0 错误
- npm run lint：0 错误 0 警告

src/app/(dashboard)/teacher/elective/page.tsx

@@ -0,0 +1,50 @@
+import { auth } from "@/auth"
+import { getElectiveCourses } from "@/modules/elective/data-access"
+import { ElectiveCourseList } from "@/modules/elective/components/elective-course-list"
+import type { ElectiveCourseStatus } from "@/modules/elective/types"
+
+export const dynamic = "force-dynamic"
+
+type SearchParams = { [key: string]: string | string[] | undefined }
+
+const getParam = (params: SearchParams, key: string) => {
+  const v = params[key]
+  return Array.isArray(v) ? v[0] : v
+}
+
+const isValidStatus = (v?: string): v is ElectiveCourseStatus =>
+  v === "draft" || v === "open" || v === "closed" || v === "cancelled"
+
+export default async function TeacherElectivePage({
+  searchParams,
+}: {
+  searchParams: Promise<SearchParams>
+}) {
+  const session = await auth()
+  const teacherId = String(session?.user?.id ?? "")
+
+  const sp = await searchParams
+  const statusParam = getParam(sp, "status")
+  const status = isValidStatus(statusParam) ? statusParam : undefined
+
+  const courses = teacherId
+    ? await getElectiveCourses({ teacherId, status })
+    : []
+
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <div className="space-y-1">
+        <h2 className="text-2xl font-bold tracking-tight">My Elective Courses</h2>
+        <p className="text-muted-foreground">
+          View and manage the elective courses you teach.
+        </p>
+      </div>
+      <ElectiveCourseList
+        courses={courses}
+        canManage
+        createHref="/admin/elective/create"
+        editHrefBuilder={(id) => `/admin/elective/${id}/edit`}
+      />
+    </div>
+  )
+}