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/stable/index.d.ts

@@ -0,0 +1,9 @@
+export as namespace stable;
+export = stable;
+
+type Comparator<T> = ((a : T, b : T)=>boolean) | ((a: T, b : T)=>number);
+
+declare function stable<T>(array : T[], comparator? : Comparator<T>) : T[];
+declare namespace stable {
+    export function inplace<T>(array: T[], comparator? : Comparator<T>) : T[];
+}