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/user-event/dist/keyboard/shared/fireInputEvent.d.ts

@@ -0,0 +1,17 @@
+import { fireEvent } from '@testing-library/dom';
+export declare function fireInputEvent(element: HTMLElement, { newValue, newSelectionStart, eventOverrides, }: {
+    newValue: string;
+    newSelectionStart: number;
+    eventOverrides: Partial<Parameters<typeof fireEvent>[1]> & {
+        [k: string]: unknown;
+    };
+}): void;
+declare const initial: unique symbol;
+declare const onBlur: unique symbol;
+declare global {
+    interface Element {
+        [initial]?: string;
+        [onBlur]?: EventListener;
+    }
+}
+export {};