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-list/list.d.ts

@@ -0,0 +1,14 @@
+type ListNode<T, K> = {
+	key: K;
+	next: undefined | ListNode<T, K>;
+	value: T;
+};
+type RootNode<T, K> = {
+	next: undefined | ListNode<T, K>;
+};
+
+export function listGetNode<T, K>(list: RootNode<T, K>, key: ListNode<T, K>['key'], isDelete?: boolean): ListNode<T, K> | undefined;
+export function listGet<T, K>(objects: undefined | RootNode<T, K>, key: ListNode<T, K>['key']): T | undefined;
+export function listSet<T, K>(objects: RootNode<T, K>, key: ListNode<T, K>['key'], value: T): void;
+export function listHas<T, K>(objects: undefined | RootNode<T, K>, key: ListNode<T, K>['key']): boolean;
+export function listDelete<T, K>(objects: undefined | RootNode<T, K>, key: ListNode<T, K>['key']): ListNode<T, K> | undefined;