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/lodash/isUndefined.js

@@ -0,0 +1,22 @@
+/**
+ * Checks if `value` is `undefined`.
+ *
+ * @static
+ * @since 0.1.0
+ * @memberOf _
+ * @category Lang
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is `undefined`, else `false`.
+ * @example
+ *
+ * _.isUndefined(void 0);
+ * // => true
+ *
+ * _.isUndefined(null);
+ * // => false
+ */
+function isUndefined(value) {
+  return value === undefined;
+}
+
+module.exports = isUndefined;