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-progressive-custom-properties/dist/matchers.d.ts

@@ -0,0 +1,33 @@
+export declare const matchers: ({
+    supports: string;
+    property: string;
+    sniff: string;
+    matchers: {
+        type: string;
+        value: string;
+        nodes: ({
+            type: string;
+            value: string;
+            isVariable?: undefined;
+        } | {
+            type: string;
+            value?: undefined;
+            isVariable?: undefined;
+        } | {
+            type: string;
+            isVariable: boolean;
+            value?: undefined;
+        })[];
+    }[];
+} | {
+    supports: string;
+    property: string;
+    sniff: string;
+    matchers: {
+        type: string;
+        value: string;
+        dimension: {
+            unit: string;
+        };
+    }[];
+})[];