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/modules/esnext.math.fscale.js

@@ -0,0 +1,13 @@
+'use strict';
+var $ = require('../internals/export');
+
+var scale = require('../internals/math-scale');
+var fround = require('../internals/math-fround');
+
+// `Math.fscale` method
+// https://rwaldron.github.io/proposal-math-extensions/
+$({ target: 'Math', stat: true, forced: true }, {
+  fscale: function fscale(x, inLow, inHigh, outLow, outHigh) {
+    return fround(scale(x, inLow, inHigh, outLow, outHigh));
+  }
+});