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/workbox-core/copyResponse.d.ts

@@ -0,0 +1,22 @@
+import './_version.js';
+/**
+ * Allows developers to copy a response and modify its `headers`, `status`,
+ * or `statusText` values (the values settable via a
+ * [`ResponseInit`]{@link https://developer.mozilla.org/en-US/docs/Web/API/Response/Response#Syntax}
+ * object in the constructor).
+ * To modify these values, pass a function as the second argument. That
+ * function will be invoked with a single object with the response properties
+ * `{headers, status, statusText}`. The return value of this function will
+ * be used as the `ResponseInit` for the new `Response`. To change the values
+ * either modify the passed parameter(s) and return it, or return a totally
+ * new object.
+ *
+ * This method is intentionally limited to same-origin responses, regardless of
+ * whether CORS was used or not.
+ *
+ * @param {Response} response
+ * @param {Function} modifier
+ * @memberof workbox-core
+ */
+declare function copyResponse(response: Response, modifier?: (responseInit: ResponseInit) => ResponseInit): Promise<Response>;
+export { copyResponse };