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/features/room-nav/RoomNavCategoryButton.tsx

@@ -10,6 +10,7 @@ export const RoomNavCategoryButton = as<'button', { closed?: boolean }>(
       className={classNames(css.CategoryButton, className)}
       variant="Background"
       radii="Pill"
+      data-nav-category-btn=""
       before={
         <Icon
           className={css.CategoryButtonIcon}