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/side-channel-weakmap/index.d.ts

@@ -0,0 +1,15 @@
+declare namespace getSideChannelWeakMap {
+	type Channel<K, V> = {
+		assert: (key: K) => void;
+		has: (key: K) => boolean;
+		get: (key: K) => V | undefined;
+		set: (key: K, value: V) => void;
+		delete: (key: K) => boolean;
+	}
+}
+
+declare function getSideChannelWeakMap<K, V>(): getSideChannelWeakMap.Channel<K, V>;
+
+declare const x: false | typeof getSideChannelWeakMap;
+
+export = x;