feat(attendance,elective): 考勤与选修课模块审计重构 — P0 修复 + i18n + Error Boundary

审计报告：docs/architecture/audit/attendance-elective-audit-report.md

P0 修复：
- attendance: getAttendanceStats 统计失真（仅基于前 20 条记录）改为 SQL 聚合查询
- attendance: getClassStudentsForAttendance 跨模块直查 classEnrollments 改为调用 classes data-access
- attendance: update/delete Action 新增资源归属校验（assertRecordOwnership）
- elective: update/delete/openSelection/closeSelection/runLottery Action 新增资源归属校验（assertCourseOwnership）

i18n 接入：
- 新增 attendance/elective 命名空间（zh-CN + en）
- attendance-stats-cards 接入 useTranslations
- elective-course-list/form 接入 useTranslations

类型安全（P1）：
- elective-course-form: 移除 as 断言，改用类型守卫 isSelectionMode
- elective-course-list: 移除 null as never 类型逃逸，改用泛型

Error Boundary：
- 新增 admin/teacher attendance error.tsx
- 新增 admin/student elective error.tsx

架构图同步：
- 004: 修正 attendance/elective/parent 章节的导出函数、文件清单、已知问题
- 005: 修正 actions 的 usedBy（标记无调用方的死代码）、新增 issues 字段、更新依赖矩阵

src/shared/i18n/messages/en/elective.json

@@ -0,0 +1,96 @@
+{
+  "title": {
+    "adminList": "Elective Courses",
+    "create": "Create Course",
+    "edit": "Edit Course",
+    "teacher": "My Elective Courses",
+    "student": "Course Selection"
+  },
+  "description": {
+    "adminList": "Manage elective courses, open/close selection and lottery.",
+    "teacher": "View and manage the elective courses you teach.",
+    "student": "Browse available courses and make selections."
+  },
+  "status": {
+    "draft": "Draft",
+    "open": "Open",
+    "closed": "Closed",
+    "cancelled": "Cancelled"
+  },
+  "selectionMode": {
+    "fcfs": "First Come First Served",
+    "lottery": "Lottery"
+  },
+  "selectionStatus": {
+    "selected": "Selected",
+    "enrolled": "Enrolled",
+    "waitlist": "Waitlist",
+    "dropped": "Dropped",
+    "rejected": "Rejected"
+  },
+  "fields": {
+    "name": "Course Name",
+    "subject": "Subject",
+    "teacher": "Teacher",
+    "grade": "Grade",
+    "description": "Description",
+    "capacity": "Capacity",
+    "enrolled": "Enrolled",
+    "classroom": "Classroom",
+    "schedule": "Schedule",
+    "startDate": "Start Date",
+    "endDate": "End Date",
+    "selectionStart": "Selection Start",
+    "selectionEnd": "Selection End",
+    "selectionMode": "Selection Mode",
+    "credit": "Credit"
+  },
+  "actions": {
+    "create": "Create Course",
+    "edit": "Edit",
+    "delete": "Delete",
+    "openSelection": "Open Selection",
+    "closeSelection": "Close Selection",
+    "runLottery": "Run Lottery",
+    "select": "Select",
+    "drop": "Drop",
+    "cancel": "Cancel",
+    "save": "Save"
+  },
+  "list": {
+    "empty": "No elective courses",
+    "emptyStudent": "No available courses",
+    "emptyDescription": "No elective courses have been created yet."
+  },
+  "form": {
+    "createTitle": "Create Elective Course",
+    "editTitle": "Edit Elective Course",
+    "namePlaceholder": "Enter course name",
+    "descriptionPlaceholder": "Enter course description"
+  },
+  "student": {
+    "mySelections": "My Selections",
+    "availableCourses": "Available Courses",
+    "selected": "Selected",
+    "enrolled": "Enrolled",
+    "waitlist": "Waitlist",
+    "capacityFull": "Capacity full",
+    "selectSuccess": "Course selected successfully",
+    "dropSuccess": "Course dropped successfully",
+    "confirmDrop": "Are you sure you want to drop this course?"
+  },
+  "lottery": {
+    "result": "Lottery result: {enrolled} enrolled, {waitlist} waitlisted",
+    "running": "Running lottery..."
+  },
+  "errors": {
+    "notFound": "Course not found",
+    "noOwnership": "You do not own this course",
+    "capacityFull": "Course capacity is full",
+    "alreadySelected": "You have already selected this course",
+    "selectionClosed": "Selection is closed",
+    "gradeMismatch": "Your grade does not match the course requirement",
+    "invalidForm": "Invalid form data",
+    "unexpected": "Unexpected error"
+  }
+}