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/internals/error-stack-install.js

@@ -0,0 +1,15 @@
+'use strict';
+var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
+var clearErrorStack = require('../internals/error-stack-clear');
+var ERROR_STACK_INSTALLABLE = require('../internals/error-stack-installable');
+
+// non-standard V8
+// eslint-disable-next-line es/no-nonstandard-error-properties -- safe
+var captureStackTrace = Error.captureStackTrace;
+
+module.exports = function (error, C, stack, dropEntries) {
+  if (ERROR_STACK_INSTALLABLE) {
+    if (captureStackTrace) captureStackTrace(error, C);
+    else createNonEnumerableProperty(error, 'stack', clearErrorStack(stack, dropEntries));
+  }
+};