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-arguments/index.js

@@ -0,0 +1,44 @@
+'use strict';
+
+var hasToStringTag = require('has-tostringtag/shams')();
+var callBound = require('call-bound');
+
+var $toString = callBound('Object.prototype.toString');
+
+/** @type {import('.')} */
+var isStandardArguments = function isArguments(value) {
+	if (
+		hasToStringTag
+		&& value
+		&& typeof value === 'object'
+		&& Symbol.toStringTag in value
+	) {
+		return false;
+	}
+	return $toString(value) === '[object Arguments]';
+};
+
+/** @type {import('.')} */
+var isLegacyArguments = function isArguments(value) {
+	if (isStandardArguments(value)) {
+		return true;
+	}
+	return value !== null
+		&& typeof value === 'object'
+		&& 'length' in value
+		&& typeof value.length === 'number'
+		&& value.length >= 0
+		&& $toString(value) !== '[object Array]'
+		&& 'callee' in value
+		&& $toString(value.callee) === '[object Function]';
+};
+
+var supportsStandardArguments = (function () {
+	return isStandardArguments(arguments);
+}());
+
+// @ts-expect-error TODO make this not error
+isStandardArguments.isLegacyArguments = isLegacyArguments; // for tests
+
+/** @type {import('.')} */
+module.exports = supportsStandardArguments ? isStandardArguments : isLegacyArguments;