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/eslint/messages/shared.js

@@ -0,0 +1,18 @@
+/**
+ * @fileoverview Shared utilities for error messages.
+ * @author Josh Goldberg
+ */
+
+"use strict";
+
+/**
+ * Converts a value to a string that may be printed in errors.
+ * @param {any} value The invalid value.
+ * @param {number} indentation How many spaces to indent
+ * @returns {string} The value, stringified.
+ */
+function stringifyValueForError(value, indentation) {
+    return value ? JSON.stringify(value, null, 4).replace(/\n/gu, `\n${" ".repeat(indentation)}`) : `${value}`;
+}
+
+module.exports = { stringifyValueForError };