refactor: 移动端升级 Vue3 + uView Plus

将 lilishop-uniapp 从 Vue2/uView 1.6 迁移到 Vue3/uview-plus，优先支持 H5/微商城与微信小程序；移除 vendored uview-ui，改用 npm 依赖、Vuex4 与迁移脚本/补丁，并补充 VUE3_MIGRATION.md 回归清单。

Co-authored-by: Cursor <cursoragent@cursor.com>

utils/mpShare.js

@@ -0,0 +1,16 @@
+export default {
+  onLoad() {
+    if (!uni.$u) {
+      uni.$u = {}
+    }
+    uni.$u.mpShare = {
+      title: '',
+      path: '',
+      imageUrl: ''
+    }
+    this.$u.mpShare = uni.$u.mpShare
+  },
+  onShareAppMessage() {
+    return this.$u.mpShare || uni.$u.mpShare
+  }
+}