refactor(school,classes): 完成 school/grade/class 审计全量改进项

P0-1/P0-2: 删除 grade-management 死模块，年级 CRUD 统一由 school 模块负责

P0-3: classes/actions.ts 从 974 行拆分为 6 个职责文件 + barrel re-export

P0-5: 13 个页面 i18n 全量接入（grades/departments/academic-year/classes/insights）

P1-1: 角色硬编码改为 hasAdminScope/hasTeacherScope/hasStudentScope 基于 dataScope.type

P1-3: 新增 SchoolErrorBoundary + SchoolListSkeleton/SchoolCardSkeleton，4 个页面包裹 Error Boundary

P1-4: classes/types.ts 跨领域类型添加归属决策注释

P1-5: schools-view.tsx 拆分为组合模式（SchoolFormDialog + SchoolDeleteDialog + SchoolListToolbar）

P1-6: 新增 getSchoolsForUser/getGradesForUser 权限感知查询函数

P2-1: 抽取 useSchoolData hook，对话框状态管理与 UI 分离

同步更新架构图文档 004/005

src/shared/i18n/messages/zh-CN/school.json

@@ -78,9 +78,51 @@
     },
     "actions": {
       "edit": "编辑",
-      "delete": "删除"
+      "delete": "删除",
+      "insights": "学情"
     },
-    "notSet": "未设置"
+    "notSet": "未设置",
+    "filters": {
+      "search": "搜索年级/学校/组长...",
+      "school": "学校",
+      "allSchools": "全部学校",
+      "head": "负责人",
+      "allHeads": "全部",
+      "missing": "两者都未设置",
+      "missingGradeHead": "未设置年级组长",
+      "missingTeachingHead": "未设置教研组长",
+      "sort": "排序",
+      "defaultSort": "默认排序",
+      "updatedDesc": "更新时间（新→旧）",
+      "updatedAsc": "更新时间（旧→新）",
+      "nameAsc": "年级名称（A→Z）",
+      "nameDesc": "年级名称（Z→A）",
+      "orderAsc": "Order（小→大）",
+      "orderDesc": "Order（大→小）",
+      "reset": "重置"
+    },
+    "list": {
+      "title": "年级列表",
+      "noSchools": "暂无学校",
+      "noSchoolsDescription": "请先创建学校，再在学校下创建年级。",
+      "noGrades": "暂无年级",
+      "noGradesDescription": "创建年级以便管理负责人和班级。",
+      "noMatch": "没有匹配结果",
+      "noMatchDescription": "尝试修改筛选条件或清空搜索。"
+    },
+    "validation": {
+      "selectSchool": "请选择学校",
+      "enterName": "请输入年级名称",
+      "nameTooLong": "年级名称最多 100 个字符",
+      "orderInvalid": "Order 必须是非负整数",
+      "duplicateName": "该学校下已存在同名年级",
+      "fixForm": "请完善表单信息",
+      "noChanges": "没有可保存的变更"
+    },
+    "optional": "可选",
+    "failedCreate": "创建年级失败",
+    "failedUpdate": "更新年级失败",
+    "failedDelete": "删除年级失败"
   },
   "departments": {
     "title": "部门管理",
@@ -159,5 +201,57 @@
       "edit": "编辑",
       "delete": "删除"
     }
+  },
+  "classManagement": {
+    "title": "班级管理",
+    "description": "管理班级并分配教师。",
+    "grade": {
+      "title": "班级管理",
+      "description": "管理你所在年级的班级。",
+      "insights": {
+        "title": "年级学情",
+        "description": "查看你负责年级的作业整体统计。",
+        "filters": "筛选",
+        "grade": "年级",
+        "apply": "应用",
+        "selectGrade": "选择年级",
+        "noGrades": "暂无负责年级",
+        "noGradesDescription": "你尚未被指派为任何年级的年级主任或教研组长。",
+        "selectToView": "请选择年级查看学情",
+        "selectToViewDescription": "选择一个年级以查看最新作业与历史成绩统计。",
+        "notFound": "年级不存在",
+        "notFoundDescription": "该年级可能不存在或暂无可访问数据。",
+        "noData": "该年级暂无作业数据",
+        "noDataDescription": "该年级学生尚未收到任何作业。",
+        "classes": "班级",
+        "students": "学生",
+        "overallAvg": "整体均分",
+        "latestAvg": "最新均分",
+        "homeworkTimeline": "作业时间线",
+        "classRanking": "班级排名",
+        "assignment": "作业",
+        "status": "状态",
+        "created": "创建时间",
+        "targeted": "目标人数",
+        "submitted": "已提交",
+        "graded": "已批改",
+        "avg": "均分",
+        "median": "中位数",
+        "class": "班级",
+        "latestAvgCol": "最新均分",
+        "prevAvg": "上次均分",
+        "delta": "变化",
+        "overallAvgCol": "整体均分",
+        "active": "活跃",
+        "inactive": "非活跃"
+      }
+    }
+  },
+  "errors": {
+    "boundary": {
+      "title": "加载失败",
+      "description": "数据加载时发生错误，请重试",
+      "retry": "重试"
+    }
   }
 }