Add Stationery and Stationery Dark themes with notebook chrome.

Manila folders, ruled chat, post-it nav, and folder tabs; dark variant uses Catppuccin Mocha colors with muted stickies and soft glows.

src/app/components/nav/NavCategory.tsx

@@ -7,5 +7,10 @@ type NavCategoryProps = {
   children: ReactNode;
 };
 export const NavCategory = as<'div', NavCategoryProps>(({ className, ...props }, ref) => (
-  <div className={classNames(css.NavCategory, className)} {...props} ref={ref} />
+  <div
+    className={classNames(css.NavCategory, className)}
+    data-nav-category=""
+    {...props}
+    ref={ref}
+  />
 ));