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/@csstools/selector-specificity/dist/index.d.ts

@@ -0,0 +1,8 @@
+import type { Node } from 'postcss-selector-parser';
+export type Specificity = {
+    a: number;
+    b: number;
+    c: number;
+};
+export declare function compare(s1: Specificity, s2: Specificity): number;
+export declare function selectorSpecificity(node: Node): Specificity;