style(StudyDetailPage): 将底部输入框的布局从sticky改为fixed

将底部输入框的布局从sticky改为fixed，以确保在滚动页面时输入框始终固定在屏幕底部，提升用户体验

@@ -124,7 +124,7 @@
                             </div>
 
                             <!-- 固定底部输入框 -->
-                            <div class="flex-none border-t px-4 py-2 bg-white sticky bottom-0 z-10">
+                            <div class="flex-none border-t px-4 py-2 bg-white fixed bottom-0 left-0 right-0 z-10">
                                 <div class="flex items-center space-x-2">
                                     <van-field v-model="popupComment" rows="1" autosize type="textarea"
                                         placeholder="请输入评论" class="flex-1 bg-gray-100 rounded-lg" />