Website restoration: Node.js backend, restored design, GitHub sync disabled

- Replaced broken .NET backend with Node.js/Express
- Restored original website design with purple gradient hero
- Updated homepage and shop pages with Bootstrap 5 responsive design
- Disabled GitHub remote sync - all code now stored locally only
- Created backup scripts and documentation
- All changes saved on Ubuntu server at /var/www/SkyArtShop

backend/node_modules/math-intrinsics/mod.js

@@ -0,0 +1,9 @@
+'use strict';
+
+var $floor = require('./floor');
+
+/** @type {import('./mod')} */
+module.exports = function mod(number, modulo) {
+	var remain = number % modulo;
+	return $floor(remain >= 0 ? remain : remain + modulo);
+};