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/style-loader/dist/runtime/insertBySelector.js

@@ -0,0 +1,34 @@
+"use strict";
+
+var memo = {};
+
+/* istanbul ignore next  */
+function getTarget(target) {
+  if (typeof memo[target] === "undefined") {
+    var styleTarget = document.querySelector(target);
+
+    // Special case to return head of iframe instead of iframe itself
+    if (window.HTMLIFrameElement && styleTarget instanceof window.HTMLIFrameElement) {
+      try {
+        // This will throw an exception if access to iframe is blocked
+        // due to cross-origin restrictions
+        styleTarget = styleTarget.contentDocument.head;
+      } catch (e) {
+        // istanbul ignore next
+        styleTarget = null;
+      }
+    }
+    memo[target] = styleTarget;
+  }
+  return memo[target];
+}
+
+/* istanbul ignore next  */
+function insertBySelector(insert, style) {
+  var target = getTarget(insert);
+  if (!target) {
+    throw new Error("Couldn't find a style target. This probably means that the value for the 'insert' parameter is invalid.");
+  }
+  target.appendChild(style);
+}
+module.exports = insertBySelector;