Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/lodash/_hashSet.js

@@ -0,0 +1,23 @@
+var nativeCreate = require('./_nativeCreate');
+
+/** Used to stand-in for `undefined` hash values. */
+var HASH_UNDEFINED = '__lodash_hash_undefined__';
+
+/**
+ * Sets the hash `key` to `value`.
+ *
+ * @private
+ * @name set
+ * @memberOf Hash
+ * @param {string} key The key of the value to set.
+ * @param {*} value The value to set.
+ * @returns {Object} Returns the hash instance.
+ */
+function hashSet(key, value) {
+  var data = this.__data__;
+  this.size += this.has(key) ? 0 : 1;
+  data[key] = (nativeCreate && value === undefined) ? HASH_UNDEFINED : value;
+  return this;
+}
+
+module.exports = hashSet;