revert: change app shell layout to non fix

This reverts commit 9630e079e8.

app/root.tsx

@@ -254,9 +254,8 @@ function Layout({ children }: React.PropsWithChildren<{}>) {
       padding="md"
       navbarOffsetBreakpoint="sm"
       asideOffsetBreakpoint="sm"
-      fixed={false}
       navbar={
-        user ? (
+        user && (
           <Navbar
             p="xs"
             hiddenBreakpoint="sm"
@@ -447,7 +446,7 @@ function Layout({ children }: React.PropsWithChildren<{}>) {
               </Navbar.Section>
             )}
           </Navbar>
-        ) : undefined
+        )
       }
       header={
         <Header height={{ base: 50, md: 70 }} p="md">