fix(desktop): use themed Toaster wrapper instead of bare sonner

#1831 fixed the Toaster wrapper to follow next-themes' resolvedTheme,
but the desktop renderer was importing `Toaster` directly from `sonner`
and never going through the wrapper. So the success toast still rendered
light on a dark UI. Switch the import to `@multica/ui/components/ui/sonner`
to match the web app and pick up the theme + icon overrides.

apps/desktop/src/renderer/src/App.tsx

@@ -7,7 +7,7 @@ import { api } from "@multica/core/api";
 import { useHasOnboarded } from "@multica/core/paths";
 import { ThemeProvider } from "@multica/ui/components/common/theme-provider";
 import { MulticaIcon } from "@multica/ui/components/common/multica-icon";
-import { Toaster } from "sonner";
+import { Toaster } from "@multica/ui/components/ui/sonner";
 import { DesktopLoginPage } from "./pages/login";
 import { DesktopShell } from "./components/desktop-layout";
 import { PageviewTracker } from "./components/pageview-tracker";