refactor: migrate chat shell to app sidebar

frontend/src/components/app-sidebar.tsx

@@ -25,6 +25,7 @@ import {
   SidebarMenuButton,
   SidebarMenuItem,
   SidebarRail,
+  SidebarTrigger,
   useSidebar,
 } from "@/components/ui/sidebar";
 
@@ -111,6 +112,7 @@ export function AppSidebar({
         <div className="brand-row">
           <span className="brand-mark" aria-hidden="true" />
           {showExpandedContent ? <strong>Jyotisha</strong> : null}
+          <SidebarTrigger placement="sidebar" />
         </div>
         <SidebarMenu>
           <SidebarMenuItem>