style(css): 优化播放按钮和标签的样式设计

简化播放按钮的样式实现，移除冗余的伪元素，改用box-shadow实现边框效果
统一标签的圆角半径和背景色，移除注释掉的代码
调整播放按钮点击逻辑，当playurl不存在时自动获取播放链接

index.html

@@ -152,7 +152,7 @@
                                 <div class="operate flexcenter">
                                     <img class="speed left" @click="fastForward('slow')" src="./static/img/speed-left.png" />
                                     <img v-if="item.state" class="play" @click="closeAll()" src="./static/img/pause-black-icon.svg" />
-                                    <img v-else class="play" @click="manageAudio(item.playurl, 'custom')" src="./static/img/play-black-icon.svg" />
+                                    <img v-else class="play" @click="item.playurl ? manageAudio(item.playurl, 'custom') : getPlayUrl(index, 'custom')" src="./static/img/play-black-icon.svg" />
                                     <img class="speed right" @click="fastForward('fast')" src="./static/img/speed-right.png" />
                                 </div>
                             </div>