refactor: Move Astro project to root directory

- Move all Astro files from dealplustech-astro/ to root
- Archive Next.js code in _nextjs-backup/
- Update .gitignore for Astro project
- Simplify project structure

This completes the migration from Next.js to Astro.
The Astro project is now at the root level.

.next/server/pages/_document.js

@@ -0,0 +1 @@
+"use strict";(()=>{var e={};e.id=660,e.ids=[660],e.modules={2785:e=>{e.exports=require("next/dist/compiled/next-server/pages.runtime.prod.js")},6689:e=>{e.exports=require("react")},997:e=>{e.exports=require("react/jsx-runtime")},1017:e=>{e.exports=require("path")}};var r=require("../webpack-runtime.js");r.C(e);var s=e=>r(r.s=e),t=r.X(0,[682],()=>s(1682));module.exports=t})();