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/dotenv-expand/index.d.ts

@@ -0,0 +1,15 @@
+export = dotenv_expand;
+
+interface DotenvResult {
+    error?: Error;
+    parsed?: {
+        [name: string]: string;
+    };
+}
+
+declare function dotenv_expand(config: DotenvResult): DotenvResult;
+
+declare namespace dotenv_expand {
+    const prototype: {
+    };
+}