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/isInteger.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var $abs = require('./abs');
+var $floor = require('./floor');
+
+var $isNaN = require('./isNaN');
+var $isFinite = require('./isFinite');
+
+/** @type {import('./isInteger')} */
+module.exports = function isInteger(argument) {
+	if (typeof argument !== 'number' || $isNaN(argument) || !$isFinite(argument)) {
+		return false;
+	}
+	var absValue = $abs(argument);
+	return $floor(absValue) === absValue;
+};