feat(student): 完成 student 模块 v4 剩余修复

- P1-4.2: 新增班级详情页 courses/[classId]，展示教师/学校/教室信息与课表

- P2-2.5: 今日课表卡片高亮当前/下一节课（useMemo 实时计算）

- P2-3.9: 作业作答进度网格支持点击跳转题目（scrollIntoView）

- P2-3.10: 作业复习视图显示正确答案（选择/判断/文本题）

- P2-4.4: 课程列表支持按班级名/教师/学校搜索

- P2-5.2: 成绩页新增趋势折线图组件 GradeTrendCard

- P2-9.2/9.3: 诊断报告新增历史记录卡片与弱点练习入口

- P2-10.2: 选课列表支持搜索与选课模式筛选

- P2-11.3: 修复教材阅读页全屏溢出

- P3-1.5: 面包屑保留首个角色段作为根上下文

- P3-7.3: 课表项支持点击跳转至班级详情页（ScheduleList href）

src/app/(dashboard)/student/learning/textbooks/[id]/loading.tsx

@@ -2,14 +2,14 @@ import { Skeleton } from "@/shared/components/ui/skeleton"
 
 export default function Loading() {
   return (
-    <div className="flex h-[calc(100vh-4rem)] flex-col overflow-hidden">
+    <div className="flex h-[calc(100vh-4rem-3rem)] flex-col overflow-hidden">
       <div className="flex items-center justify-between border-b py-3 px-6 shrink-0">
         <div className="flex items-center gap-3">
           <Skeleton className="h-6 w-48" />
           <Skeleton className="h-5 w-16 rounded-full" />
         </div>
       </div>
-      <div className="flex-1 p-6">
+      <div className="flex-1">
         <Skeleton className="h-full w-full" />
       </div>
     </div>

src/app/(dashboard)/student/learning/textbooks/[id]/page.tsx

@@ -29,7 +29,7 @@ export default async function StudentTextbookDetailPage({
   if (!textbook) notFound()
 
   return (
-    <div className="flex h-[calc(100vh-4rem)] flex-col overflow-hidden bg-muted/5">
+    <div className="flex h-[calc(100vh-4rem-3rem)] flex-col overflow-hidden bg-muted/5">
       <div className="flex items-center justify-between border-b bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60 py-3 px-6 shrink-0 z-10">
         <div className="flex items-center gap-3 min-w-0">
           <h1 className="text-lg font-bold tracking-tight truncate">{textbook.title}</h1>
@@ -43,7 +43,7 @@ export default async function StudentTextbookDetailPage({
         </div>
       </div>
 
-      <div className="flex-1 overflow-hidden p-6">
+      <div className="flex-1 overflow-hidden">
         {chapters.length === 0 ? (
           <div className="h-full flex items-center justify-center rounded-lg border border-dashed bg-card">
             <EmptyState