refactor(manager): 优化全局空状态、错误图片占位并升级遗留消息语法

- 增加表格与树组件全局空状态 (el-empty) 样式规范
- 补齐视图图片语义化 alt，并添加全局图片加载异常 SVG 占位兜底
- 将砍价/秒杀/自定义面板中的 $Message 兼容语法替换为 ElMessage
- 清理冗余依赖 vuex，将 sass-loader 调整至 devDependencies

manager/src/main.js

@@ -8,6 +8,7 @@ import { router } from "./router/index";
 import i18n from "@/locale";
 import { setupElementPlus } from "@/plugins/element";
 import { setupLegacyMessage } from "@/utils/message";
+import { setupImgFallback } from "@/utils/imgFallback";
 import liliDialog from "@/components/lili-dialog";
 import PriceColorScheme from "@/components/price-color-scheme.vue";
 import { install as installVueQr } from "vue-qr";
@@ -43,6 +44,7 @@ const app = createApp(App);
 
 setupElementPlus(app);
 setupLegacyMessage(app);
+setupImgFallback();
 installVueQr(app);
 
 app.use(router);