fix(StudyDetailPage): 调整学习资料弹窗样式和关闭逻辑

将弹窗位置从右侧改为底部，允许点击遮罩关闭
移除返回按钮，改用关闭图标按钮

@@ -444,9 +444,9 @@
         <!-- 学习资料全屏弹窗 -->
         <van-popup
             v-model:show="showMaterialsPopup"
-            position="right"
+            position="bottom"
             :style="{ width: '100%', height: '100%' }"
-            :close-on-click-overlay="false"
+            :close-on-click-overlay="true"
             :lock-scroll="true"
         >
             <div class="flex flex-col h-full bg-gray-50">
@@ -454,16 +454,16 @@
                 <div class="bg-white shadow-sm border-b border-gray-100">
                     <div class="flex items-center justify-between px-4 py-3">
                         <div class="flex items-center gap-3">
-                            <van-button
+                            <!-- <van-button
                                 @click="showMaterialsPopup = false"
                                 type="default"
                                 size="small"
                                 round
                                 class="w-8 h-8 p-0 bg-gray-100 border-0"
                             >
-                                <van-icon name="arrow-left" size="16" class="text-gray-600" />
-                            </van-button>
-                            <div>
+                                <van-icon name="cross" size="16" class="text-gray-600" />
+                            </van-button> -->
+                            <div class="px-1">
                                 <h2 class="text-lg font-medium text-gray-900">学习资料</h2>
                                 <p class="text-xs text-gray-500">
                                     共 {{ courseFile?.list ? courseFile.list.length : 0 }} 个文件
@@ -471,9 +471,18 @@
                             </div>
                         </div>
                         <div class="px-2 py-1 bg-blue-50 rounded-full">
-                            <span class="text-blue-600 text-sm font-medium">
+                            <!-- <span class="text-blue-600 text-sm font-medium">
                                 {{ courseFile?.list ? courseFile.list.length : 0 }}
-                            </span>
+                            </span> -->
+                            <van-button
+                                @click="showMaterialsPopup = false"
+                                type="default"
+                                size="small"
+                                round
+                                class="w-8 h-8 p-0 bg-gray-100 border-0"
+                            >
+                                <van-icon name="cross" size="16" class="text-gray-600" />
+                            </van-button>
                         </div>
                     </div>
                 </div>