refactor(admin): simplify entry route to point to dashboard

The `/admin` route now directly serves the dashboard page by adding an alias, removing the need for a separate login page at that path.

- Deletes `pages/admin/index.vue` and the `admin-login` layout.
- Aliases `/admin` to `/admin/dashboard` for a more direct entry point.
- Improves the default layout with a sticky footer.
- Updates VSCode settings for better Tailwind CSS IntelliSense.

app/pages/admin/dashboard/index.vue

@@ -19,6 +19,7 @@ const pageTitle = "仪表盘"
 definePageMeta({
   layout: "admin-dashboard",
   title: pageTitle,
+  alias: ['/admin']
 })
 useHead({
   title: pageTitle