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/is-symbol/index.js

@@ -0,0 +1,40 @@
+'use strict';
+
+var callBound = require('call-bound');
+var $toString = callBound('Object.prototype.toString');
+var hasSymbols = require('has-symbols')();
+var safeRegexTest = require('safe-regex-test');
+
+if (hasSymbols) {
+	var $symToStr = callBound('Symbol.prototype.toString');
+	var isSymString = safeRegexTest(/^Symbol\(.*\)$/);
+
+	/** @type {(value: object) => value is Symbol} */
+	var isSymbolObject = function isRealSymbolObject(value) {
+		if (typeof value.valueOf() !== 'symbol') {
+			return false;
+		}
+		return isSymString($symToStr(value));
+	};
+
+	/** @type {import('.')} */
+	module.exports = function isSymbol(value) {
+		if (typeof value === 'symbol') {
+			return true;
+		}
+		if (!value || typeof value !== 'object' || $toString(value) !== '[object Symbol]') {
+			return false;
+		}
+		try {
+			return isSymbolObject(value);
+		} catch (e) {
+			return false;
+		}
+	};
+} else {
+	/** @type {import('.')} */
+	module.exports = function isSymbol(value) {
+		// this environment does not support Symbols.
+		return false && value;
+	};
+}