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/sidebar/SidebarContent.tsx

@@ -8,10 +8,10 @@ type SidebarContentProps = {
 export function SidebarContent({ scrollable, sticky }: SidebarContentProps) {
   return (
     <>
-      <Box direction="Column" grow="Yes">
+      <Box direction="Column" grow="Yes" data-sidebar-scroll-region="" style={{ overflow: 'visible', minWidth: 0 }}>
         {scrollable}
       </Box>
-      <Box direction="Column" shrink="No">
+      <Box direction="Column" shrink="No" data-sidebar-sticky="" style={{ overflow: 'visible' }}>
         {sticky}
       </Box>
     </>