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/webpack/lib/AbstractMethodError.js

@@ -0,0 +1,55 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Ivan Kopeykin @vankop
+*/
+
+"use strict";
+
+const WebpackError = require("./WebpackError");
+
+const CURRENT_METHOD_REGEXP = /at ([a-zA-Z0-9_.]*)/;
+
+/**
+ * @param {string=} method method name
+ * @returns {string} message
+ */
+function createMessage(method) {
+	return `Abstract method${method ? ` ${method}` : ""}. Must be overridden.`;
+}
+
+/**
+ * @constructor
+ */
+function Message() {
+	/** @type {string | undefined} */
+	this.stack = undefined;
+	Error.captureStackTrace(this);
+	/** @type {RegExpMatchArray | null} */
+	const match =
+		/** @type {string} */
+		(/** @type {unknown} */ (this.stack))
+			.split("\n")[3]
+			.match(CURRENT_METHOD_REGEXP);
+
+	this.message = match && match[1] ? createMessage(match[1]) : createMessage();
+}
+
+/**
+ * Error for abstract method
+ * @example
+ * ```js
+ * class FooClass {
+ *     abstractMethod() {
+ *         throw new AbstractMethodError(); // error message: Abstract method FooClass.abstractMethod. Must be overridden.
+ *     }
+ * }
+ * ```
+ */
+class AbstractMethodError extends WebpackError {
+	constructor() {
+		super(new Message().message);
+		this.name = "AbstractMethodError";
+	}
+}
+
+module.exports = AbstractMethodError;