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/@testing-library/jest-dom/dist/to-be-in-the-document.js

@@ -0,0 +1,29 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.toBeInTheDocument = toBeInTheDocument;
+var _utils = require("./utils");
+function toBeInTheDocument(element) {
+  if (element !== null || !this.isNot) {
+    (0, _utils.checkHtmlElement)(element, toBeInTheDocument, this);
+  }
+  const pass = element === null ? false : element.ownerDocument === element.getRootNode({
+    composed: true
+  });
+  const errorFound = () => {
+    return `expected document not to contain element, found ${this.utils.stringify(element.cloneNode(true))} instead`;
+  };
+  const errorNotFound = () => {
+    return `element could not be found in the document`;
+  };
+  return {
+    pass,
+    message: () => {
+      return [this.utils.matcherHint(`${this.isNot ? '.not' : ''}.toBeInTheDocument`, 'element', ''), '',
+      // eslint-disable-next-line @babel/new-cap
+      this.utils.RECEIVED_COLOR(this.isNot ? errorFound() : errorNotFound())].join('\n');
+    }
+  };
+}