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/cache/config.json

@@ -0,0 +1,7 @@
+{
+	"telemetry": {
+		"notifiedAt": "1772339974492",
+		"anonymousId": "40842ad6f367c80c9d1ba4d4fdb61a47fcc5db1ee6eb341fb94525a5dc9ff332",
+		"salt": "fdc933f5780ef52d1b1188424192932a"
+	}
+}