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/@isaacs/cliui/index.mjs

@@ -0,0 +1,14 @@
+// Bootstrap cliui with ESM dependencies:
+import { cliui } from './build/lib/index.js'
+
+import stringWidth from 'string-width'
+import stripAnsi from 'strip-ansi'
+import wrap from 'wrap-ansi'
+
+export default function ui (opts) {
+  return cliui(opts, {
+    stringWidth,
+    stripAnsi,
+    wrap
+  })
+}