fix(ui): close sidebar on mobile when opening Calendar from user menu (#26979)

Every other navigation entry in the user menu (Settings, Admin Panel,
Archived Chats, Workspace, Notes, Automations, Playground, Sign Out)
collapses the sidebar on mobile after navigating, but the Calendar entry
was missing this handling, leaving the sidebar open over the Calendar
page on mobile. Add the same mobile guard used by the sibling entries.

src/lib/components/layout/Sidebar/UserMenu.svelte

@@ -337,6 +337,10 @@
 							e.preventDefault();
 							show = false;
 							goto('/calendar');
+							if ($mobile) {
+								await tick();
+								showSidebar.set(false);
+							}
 						}}
 					>
 						<div class="self-center">