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/yargs/build/lib/utils/set-blocking.js

@@ -0,0 +1,12 @@
+export default function setBlocking(blocking) {
+    if (typeof process === 'undefined')
+        return;
+    [process.stdout, process.stderr].forEach(_stream => {
+        const stream = _stream;
+        if (stream._handle &&
+            stream.isTTY &&
+            typeof stream._handle.setBlocking === 'function') {
+            stream._handle.setBlocking(blocking);
+        }
+    });
+}