feat(admin): implement initial admin dashboard and member management

This commit introduces the foundational structure for the admin dashboard, focusing on the member management feature.
Key additions include:

- A new page at `/admin/manage/members` to display and manage members.
- An `AddModal` component with a comprehensive form for creating new members, featuring validation with Zod and input
masking.
- A reusable `PhoneInput` component with country code selection, backed by a new `useCountries` composable and a full
country dataset.
- A custom, user-friendly global error page (`error.vue`) to handle application errors gracefully.
- Updated dashboard sidebar navigation to include the new member management section.
- Added recommended VS Code extensions and settings to improve developer experience.

.vscode/admin-templates.vue

@@ -0,0 +1,27 @@
+<template>
+  <UDashboardPanel>
+    <template #header>
+      <UDashboardNavbar :title="pageTitle" toggle>
+        <template #leading>
+          <UDashboardSidebarCollapse />
+        </template>
+      </UDashboardNavbar>
+    </template>
+    <template #body>
+      管理员界面模板
+    </template>
+  </UDashboardPanel>
+</template>
+
+<script lang="ts" setup>
+const pageTitle = "管理员界面模板"
+definePageMeta({
+  layout: "admin-dashboard",
+  title: pageTitle
+})
+useHead({
+  title: pageTitle
+})
+</script>
+
+<style></style>