refactor: RBAC权限系统重构 + UI组件拆分 + 测试修复 + 架构文档

- RBAC: 新增30个权限点、DataScope行级权限、requirePermission守卫，所有57+ Server Action接入权限校验
- UI拆分: exam-form(1623行→11文件)、textbook-reader(744行→7文件)，均降至300行以内
- 测试: 新增5个单元测试文件(19用例)，修复4个集成测试文件(38用例全部通过)
- 架构文档: 新增架构影响地图(004/005)、标准功能清单(006)、差距审计报告(007)
- 项目规则: 架构图优先规则，改码必同步图
- 安全: rehype-sanitize净化、AES加密API Key、权限路由守卫
- 无障碍: skip-link、aria-label、prefers-reduced-motion
- 性能: next/font优化、next/image、代码分割

src/app/(dashboard)/teacher/homework/assignments/create/page.tsx

@@ -2,12 +2,14 @@ import { HomeworkAssignmentForm } from "@/modules/homework/components/homework-a
 import { getExams } from "@/modules/exams/data-access"
 import { getTeacherClasses } from "@/modules/classes/data-access"
 import { EmptyState } from "@/shared/components/ui/empty-state"
+import { getAuthContext } from "@/shared/lib/auth-guard"
 import { FileQuestion } from "lucide-react"
 
 export const dynamic = "force-dynamic"
 
 export default async function CreateHomeworkAssignmentPage() {
-  const [exams, classes] = await Promise.all([getExams({}), getTeacherClasses()])
+  const { dataScope } = await getAuthContext()
+  const [exams, classes] = await Promise.all([getExams({ scope: dataScope }), getTeacherClasses()])
   const options = exams.map((e) => ({ id: e.id, title: e.title }))
 
   return (