fix(tui): show toast when variant_list keybind used with no variants

packages/opencode/src/cli/cmd/tui/app.tsx

@@ -715,6 +715,13 @@ function App(props: { onSnapshot?: () => Promise<string[]> }) {
         hidden: local.model.variant.list().length === 0,
         slashName: "variants",
         run: () => {
+          if (local.model.variant.list().length === 0) {
+            return toast.show({
+              title: "No variants available",
+              message: "The current model does not support any variants.",
+              variant: "info",
+            })
+          }
           dialog.replace(() => <DialogVariant />)
         },
       },