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/internals/queue.js

@@ -0,0 +1,25 @@
+'use strict';
+var Queue = function () {
+  this.head = null;
+  this.tail = null;
+};
+
+Queue.prototype = {
+  add: function (item) {
+    var entry = { item: item, next: null };
+    var tail = this.tail;
+    if (tail) tail.next = entry;
+    else this.head = entry;
+    this.tail = entry;
+  },
+  get: function () {
+    var entry = this.head;
+    if (entry) {
+      var next = this.head = entry.next;
+      if (next === null) this.tail = null;
+      return entry.item;
+    }
+  }
+};
+
+module.exports = Queue;