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-have-attribute.js

@@ -0,0 +1,31 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.toHaveAttribute = toHaveAttribute;
+var _utils = require("./utils");
+function printAttribute(stringify, name, value) {
+  return value === undefined ? name : `${name}=${stringify(value)}`;
+}
+function getAttributeComment(stringify, name, value) {
+  return value === undefined ? `element.hasAttribute(${stringify(name)})` : `element.getAttribute(${stringify(name)}) === ${stringify(value)}`;
+}
+function toHaveAttribute(htmlElement, name, expectedValue) {
+  (0, _utils.checkHtmlElement)(htmlElement, toHaveAttribute, this);
+  const isExpectedValuePresent = expectedValue !== undefined;
+  const hasAttribute = htmlElement.hasAttribute(name);
+  const receivedValue = htmlElement.getAttribute(name);
+  return {
+    pass: isExpectedValuePresent ? hasAttribute && this.equals(receivedValue, expectedValue) : hasAttribute,
+    message: () => {
+      const to = this.isNot ? 'not to' : 'to';
+      const receivedAttribute = hasAttribute ? printAttribute(this.utils.stringify, name, receivedValue) : null;
+      const matcher = this.utils.matcherHint(`${this.isNot ? '.not' : ''}.toHaveAttribute`, 'element', this.utils.printExpected(name), {
+        secondArgument: isExpectedValuePresent ? this.utils.printExpected(expectedValue) : undefined,
+        comment: getAttributeComment(this.utils.stringify, name, expectedValue)
+      });
+      return (0, _utils.getMessage)(this, matcher, `Expected the element ${to} have attribute`, printAttribute(this.utils.stringify, name, expectedValue), 'Received', receivedAttribute);
+    }
+  };
+}