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-bigint/index.js

@@ -0,0 +1,41 @@
+'use strict';
+
+var hasBigInts = require('has-bigints')();
+
+if (hasBigInts) {
+	var bigIntValueOf = BigInt.prototype.valueOf;
+	/** @type {(value: object) => value is BigInt} */
+	var tryBigInt = function tryBigIntObject(value) {
+		try {
+			bigIntValueOf.call(value);
+			return true;
+		} catch (e) {
+		}
+		return false;
+	};
+
+	/** @type {import('.')} */
+	module.exports = function isBigInt(value) {
+		if (
+			value === null
+			|| typeof value === 'undefined'
+			|| typeof value === 'boolean'
+			|| typeof value === 'string'
+			|| typeof value === 'number'
+			|| typeof value === 'symbol'
+			|| typeof value === 'function'
+		) {
+			return false;
+		}
+		if (typeof value === 'bigint') {
+			return true;
+		}
+
+		return tryBigInt(value);
+	};
+} else {
+	/** @type {import('.')} */
+	module.exports = function isBigInt(value) {
+		return false && value;
+	};
+}