Added this stupid vibecoded app as a test

LaDOSE.Src/LaDOSE.WebApp/src/lib/api/errors.ts

@@ -0,0 +1,21 @@
+import { goto } from '$app/navigation';
+import { session } from '$lib/stores/session.svelte';
+import { ApiError } from './client';
+
+/**
+ * Turns a failed call into something to show the user.
+ *
+ * A 401 means the 16-minute JWT lapsed mid-session: there is nothing useful to
+ * display, so the session is dropped and the user is sent back to `/login`, and
+ * this returns null.
+ */
+export function toErrorMessage(cause: unknown, fallback: string): string | null {
+	if (cause instanceof ApiError && cause.status === 401) {
+		session.clear();
+		void goto('/login', { replaceState: true });
+		return null;
+	}
+
+	// ApiError already carries the API's own `message`, or "unreachable" for status 0.
+	return cause instanceof ApiError ? cause.message : fallback;
+}