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/domexception/lib/DOMException-impl.js

@@ -0,0 +1,22 @@
+"use strict";
+const legacyErrorCodes = require("./legacy-error-codes.json");
+const idlUtils = require("./utils.js");
+
+exports.implementation = class DOMExceptionImpl {
+  constructor(globalObject, [message, name]) {
+    this.name = name;
+    this.message = message;
+  }
+
+  get code() {
+    return legacyErrorCodes[this.name] || 0;
+  }
+};
+
+// A proprietary V8 extension that causes the stack property to appear.
+exports.init = impl => {
+  if (Error.captureStackTrace) {
+    const wrapper = idlUtils.wrapperForImpl(impl);
+    Error.captureStackTrace(wrapper, wrapper.constructor);
+  }
+};