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)/student/diagnostic/page.tsx

@@ -0,0 +1,31 @@
+import { Stethoscope } from "lucide-react"
+import { getAuthContext } from "@/shared/lib/auth-guard"
+import { getStudentMasterySummary } from "@/modules/diagnostic/data-access"
+import { getDiagnosticReports } from "@/modules/diagnostic/data-access-reports"
+import { StudentDiagnosticView } from "@/modules/diagnostic/components/student-diagnostic-view"
+
+export const dynamic = "force-dynamic"
+
+export default async function StudentDiagnosticPage() {
+  const ctx = await getAuthContext()
+
+  const [summary, reports] = await Promise.all([
+    getStudentMasterySummary(ctx.userId),
+    getDiagnosticReports({ studentId: ctx.userId }),
+  ])
+
+  return (
+    <div className="h-full flex-1 flex-col space-y-8 p-8 md:flex">
+      <div>
+        <h2 className="flex items-center gap-2 text-2xl font-bold tracking-tight">
+          <Stethoscope className="h-6 w-6" />
+          My Diagnostic
+        </h2>
+        <p className="text-muted-foreground">
+          Your knowledge point mastery analysis and diagnostic reports.
+        </p>
+      </div>
+      <StudentDiagnosticView summary={summary} reports={reports} />
+    </div>
+  )
+}

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

@@ -0,0 +1,49 @@
+import { auth } from "@/auth"
+import { Inbox } from "lucide-react"
+
+import { getAvailableCoursesForStudent, getStudentSelections } from "@/modules/elective/data-access-selections"
+import { StudentSelectionView } from "@/modules/elective/components/student-selection-view"
+import { EmptyState } from "@/shared/components/ui/empty-state"
+
+export const dynamic = "force-dynamic"
+
+export default async function StudentElectivePage() {
+  const session = await auth()
+  const studentId = String(session?.user?.id ?? "")
+
+  if (!studentId) {
+    return (
+      <div className="flex h-full flex-col space-y-8 p-8">
+        <div>
+          <h2 className="text-2xl font-bold tracking-tight">Elective Courses</h2>
+          <p className="text-muted-foreground">Browse and select elective courses.</p>
+        </div>
+        <EmptyState
+          title="Sign in required"
+          description="Please sign in to view elective courses."
+          icon={Inbox}
+        />
+      </div>
+    )
+  }
+
+  const [availableCourses, mySelections] = await Promise.all([
+    getAvailableCoursesForStudent(studentId),
+    getStudentSelections(studentId),
+  ])
+
+  return (
+    <div className="flex h-full flex-col space-y-8 p-8">
+      <div>
+        <h2 className="text-2xl font-bold tracking-tight">Elective Courses</h2>
+        <p className="text-muted-foreground">
+          Browse available electives and manage your selections.
+        </p>
+      </div>
+      <StudentSelectionView
+        availableCourses={availableCourses}
+        mySelections={mySelections}
+      />
+    </div>
+  )
+}