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/getEventProps.d.ts

@@ -0,0 +1,17 @@
+import { keyboardKey, keyboardState } from './types';
+export declare function getKeyEventProps(keyDef: keyboardKey, state: keyboardState): {
+    key: string | undefined;
+    code: string | undefined;
+    altKey: boolean;
+    ctrlKey: boolean;
+    metaKey: boolean;
+    shiftKey: boolean;
+    /** @deprecated use code instead */
+    keyCode: number | undefined;
+};
+export declare function getMouseEventProps(state: keyboardState): {
+    altKey: boolean;
+    ctrlKey: boolean;
+    metaKey: boolean;
+    shiftKey: boolean;
+};