feat(classes): optimize teacher dashboard ui and implement grade management

src/modules/homework/components/homework-assignment-exam-preview-pane.tsx

@@ -20,15 +20,19 @@ export function HomeworkAssignmentExamPreviewPane({
   onQuestionSelect: (questionId: string) => void
 }) {
   return (
-    <div className="md:col-span-2 flex h-full flex-col overflow-hidden rounded-md border bg-card">
-      <div className="border-b px-4 py-3 text-sm font-medium">题目</div>
-      <ScrollArea className="flex-1 p-4">
-        <ExamViewer
-          structure={structure}
-          questions={questions}
-          selectedQuestionId={selectedQuestionId}
-          onQuestionSelect={onQuestionSelect}
-        />
+    <div className="md:col-span-2 flex h-full flex-col overflow-hidden">
+      <div className="border-b px-6 py-4 bg-muted/5 flex items-center justify-between">
+        <span className="text-sm font-medium">Question Preview</span>
+      </div>
+      <ScrollArea className="flex-1 bg-background">
+        <div className="p-6">
+          <ExamViewer
+            structure={structure}
+            questions={questions}
+            selectedQuestionId={selectedQuestionId}
+            onQuestionSelect={onQuestionSelect}
+          />
+        </div>
       </ScrollArea>
     </div>
   )