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/thunky/promise.js

@@ -0,0 +1,20 @@
+module.exports = thunkyp
+
+function thunkyp (fn) {
+  let running = null
+
+  return ready
+
+  function ready () {
+    if (running) return running
+    const p = fn()
+    if (!(p instanceof Promise)) running = Promise.resolve(p)
+    else running = p
+    running.catch(onerror)
+    return running
+  }
+
+  function onerror () {
+    running = null
+  }
+}