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/postcss-stepped-value-functions/dist/utils.d.ts

@@ -0,0 +1,8 @@
+import valueParser from 'postcss-value-parser';
+import type { FunctionNode, Node, WordNode } from 'postcss-value-parser';
+import type { Declaration, Result } from 'postcss';
+import { pluginOptions } from './index';
+export declare function isVarNode(node: Node): boolean;
+export declare function validateArgumentsAndTypes(node: FunctionNode, decl: Declaration, result: Result, options: pluginOptions): valueParser.Dimension[] | undefined;
+export declare function optionallyWarn(decl: Declaration, result: Result, message: string, options: pluginOptions): void;
+export declare function functionNodeToWordNode(fn: FunctionNode): WordNode;