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/y18n/build/lib/platform-shims/node.js

@@ -0,0 +1,19 @@
+import { readFileSync, statSync, writeFile } from 'fs';
+import { format } from 'util';
+import { resolve } from 'path';
+export default {
+    fs: {
+        readFileSync,
+        writeFile
+    },
+    format,
+    resolve,
+    exists: (file) => {
+        try {
+            return statSync(file).isFile();
+        }
+        catch (err) {
+            return false;
+        }
+    }
+};