style: fix spacing and clean up unused styles

remove the unused CustomEmpty scss stylesheet
inline the empty image dimensions in CustomEmpty component and remove unused mode attribute
replace mt-8 utility classes with explicit mt-[8px] across multiple components
remove the deprecated style import in CustomEmpty

src/pages/home/components/AnswerComponent/index.vue

@@ -13,7 +13,7 @@
         <ChatMarkdown :text="processedContent" />
       </div>
       <!-- 超过3行时显示...提示 -->
-      <div v-if="!finish" class="flex flex-row items-center mt-8">
+      <div v-if="!finish" class="flex flex-row items-center mt-[8px]">
         <span class="text-[12px] font-normal font-color-600">正在生成</span>
         <ChatLoading />
       </div>