fix(SharePoster): 修改分享海报标题为分享课程并移除关闭按钮

移除冗余的关闭按钮以简化界面，同时将标题从“分享海报”更改为“分享课程”以更准确地描述功能

@@ -9,7 +9,7 @@
         <div class="PosterWrapper p-4">
             <!-- 标题与关闭按钮 -->
             <div class="flex justify-between items-center mb-3">
-                <h3 class="font-medium">分享海报</h3>
+                <h3 class="font-medium">分享课程</h3>
                 <van-icon name="cross" @click="close" />
             </div>
 
@@ -44,9 +44,9 @@
 
             <!-- 底部提示与关闭按钮 -->
             <div class="mt-3 text-center text-gray-500 text-xs">长按图片保存至手机</div>
-            <div class="mt-4">
+            <!-- <div class="mt-4">
                 <button class="w-full bg-white border border-green-500 text-green-600 py-2 rounded-lg" @click="close">关闭</button>
-            </div>
+            </div> -->
         </div>
     </van-popup>
     <van-back-top right="5vw" bottom="25vh" offset="600" />