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/css-tree/lib/syntax/node/Number.js

@@ -0,0 +1,18 @@
+var NUMBER = require('../../tokenizer').TYPE.Number;
+
+module.exports = {
+    name: 'Number',
+    structure: {
+        value: String
+    },
+    parse: function() {
+        return {
+            type: 'Number',
+            loc: this.getLocation(this.scanner.tokenStart, this.scanner.tokenEnd),
+            value: this.consume(NUMBER)
+        };
+    },
+    generate: function(node) {
+        this.chunk(node.value);
+    }
+};