refactor: 四端完成 Options API → script setup + vuex → pinia 迁移

- buyer(95) / seller(169) / im(53) / manager(280) 共 597 个组件全部从 Options API 转换为 <script setup>
- 四端 vuex 全部移除，状态管理统一迁移至 pinia 4（stores/ 目录）
- util.js 等基础设施去除 vm 首参依赖；全局属性（$Message/$filters 等）在 script 内改为具名导入
- 被外部 ref 访问的公共组件均已补齐 defineExpose（清单见各端 MIGRATION-VUE3.md）
- 各端 eslint 启用 vue/component-api-style 防止新代码回退 Options API
- 四端 yarn build 全部通过；迁移约定与注意事项已更新至各端 MIGRATION-VUE3.md

buyer/src/stores/app.js

@@ -0,0 +1,45 @@
+import { defineStore } from "pinia";
+import storage from "@/plugins/storage.js";
+import defaultLogo from "@/assets/images/logo2.png";
+
+export const useAppStore = defineStore("app", {
+  state: () => ({
+    navList: [],
+    cartNum: storage.getItem("cartNum") || 0,
+    unreadMsg: 0,
+    logoImg: storage.getItem("logoImg") || defaultLogo,
+    siteName: storage.getItem("siteName") || "lilishop",
+    hotWordsList: storage.getItem("hotWordsList"),
+    category: (() => {
+      try {
+        const raw = localStorage.getItem("category");
+        return raw ? JSON.parse(raw) : null;
+      } catch {
+        return null;
+      }
+    })(),
+  }),
+  actions: {
+    setCategory(data) {
+      this.category = data;
+    },
+    setNavList(data) {
+      this.navList = data;
+    },
+    setCartNum(data) {
+      this.cartNum = data;
+    },
+    setUnreadMsg(data) {
+      this.unreadMsg = Number(data) || 0;
+    },
+    setHotWords(data) {
+      this.hotWordsList = data;
+    },
+    setLogoImg(data) {
+      this.logoImg = data;
+    },
+    setSiteName(data) {
+      this.siteName = data;
+    },
+  },
+});