ui(layout): top-bar user menu width parity with sidebar overflow

W4a item 2 promoted DropdownMenuItem to whitespace-nowrap globally and
bumped the sidebar user menu to w-60 so the German "Benachrichtigungs-
Center" label stayed on a single line. The top-bar user menu kept its
w-48 (192 px) width — the same label plus a 16 px icon + 8 px gap + 16
px padding measures ~220 px and overflowed under the global nowrap +
overflow-x-hidden, clipping without an ellipsis.

Bump the top-bar user menu to w-60 so it matches the sidebar's symmetry.

src/components/layout/top-bar.tsx

@@ -81,7 +81,7 @@ export function TopBar() {
               <span className="hidden sm:inline">{user.username}</span>
               <ChevronDown className="h-3 w-3 opacity-60" />
             </DropdownMenuTrigger>
-            <DropdownMenuContent align="end" className="w-48">
+            <DropdownMenuContent align="end" className="w-60">
               <DropdownMenuItem asChild>
                 <Link href="/settings/account" className="cursor-pointer">
                   <Settings className="mr-2 h-4 w-4" />