test(ui): add getCookie to cookieUtils mock in user_dashboard test

user_dashboard.tsx imports getCookie from @/utils/cookieUtils, but the
vi.mock factory in user_dashboard.test.tsx only exports clearTokenCookies.
Vitest throws `No "getCookie" export is defined on the "@/utils/cookieUtils"
mock`, breaking all three beforeunload-listener tests.

Add getCookie to the mock factory so it matches the current imports.

ui/litellm-dashboard/src/components/user_dashboard.test.tsx

@@ -45,6 +45,7 @@ vi.mock("jwt-decode", () => ({
 // Mock cookie utility
 vi.mock("@/utils/cookieUtils", () => ({
   clearTokenCookies: vi.fn(),
+  getCookie: vi.fn().mockReturnValue("fake-jwt-token"),
 }));
 
 // Mock fetchTeams