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/middleware-manifest.json

@@ -0,0 +1,6 @@
+{
+  "version": 3,
+  "middleware": {},
+  "functions": {},
+  "sortedMiddleware": []
+}