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/core-js-pure/internals/symbol-constructor-detection.js

@@ -0,0 +1,19 @@
+'use strict';
+/* eslint-disable es/no-symbol -- required for testing */
+var V8_VERSION = require('../internals/environment-v8-version');
+var fails = require('../internals/fails');
+var globalThis = require('../internals/global-this');
+
+var $String = globalThis.String;
+
+// eslint-disable-next-line es/no-object-getownpropertysymbols -- required for testing
+module.exports = !!Object.getOwnPropertySymbols && !fails(function () {
+  var symbol = Symbol('symbol detection');
+  // Chrome 38 Symbol has incorrect toString conversion
+  // `get-own-property-symbols` polyfill symbols converted to object are not Symbol instances
+  // nb: Do not call `String` directly to avoid this being optimized out to `symbol+''` which will,
+  // of course, fail.
+  return !$String(symbol) || !(Object(symbol) instanceof Symbol) ||
+    // Chrome 38-40 symbols are not inherited from DOM collections prototypes to instances
+    !Symbol.sham && V8_VERSION && V8_VERSION < 41;
+});