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/react-scripts/lib/react-app.d.ts

@@ -0,0 +1,71 @@
+/// <reference types="node" />
+/// <reference types="react" />
+/// <reference types="react-dom" />
+
+declare namespace NodeJS {
+  interface ProcessEnv {
+    readonly NODE_ENV: 'development' | 'production' | 'test';
+    readonly PUBLIC_URL: string;
+  }
+}
+
+declare module '*.avif' {
+  const src: string;
+  export default src;
+}
+
+declare module '*.bmp' {
+  const src: string;
+  export default src;
+}
+
+declare module '*.gif' {
+  const src: string;
+  export default src;
+}
+
+declare module '*.jpg' {
+  const src: string;
+  export default src;
+}
+
+declare module '*.jpeg' {
+  const src: string;
+  export default src;
+}
+
+declare module '*.png' {
+  const src: string;
+  export default src;
+}
+
+declare module '*.webp' {
+    const src: string;
+    export default src;
+}
+
+declare module '*.svg' {
+  import * as React from 'react';
+
+  export const ReactComponent: React.FunctionComponent<React.SVGProps<
+    SVGSVGElement
+  > & { title?: string }>;
+
+  const src: string;
+  export default src;
+}
+
+declare module '*.module.css' {
+  const classes: { readonly [key: string]: string };
+  export default classes;
+}
+
+declare module '*.module.scss' {
+  const classes: { readonly [key: string]: string };
+  export default classes;
+}
+
+declare module '*.module.sass' {
+  const classes: { readonly [key: string]: string };
+  export default classes;
+}