fix: use window.location.origin as fallback for VITE_API_URL

Vite bakes VITE_* vars at build time, so hardcoding a URL in .env.production
breaks CI E2E which runs on localhost. Now falls back to the browser origin
at runtime, which works correctly since nginx reverse-proxies /api to the
local API container.

Fixes GRO-1280.

apps/web/src/lib/auth-client.ts

@@ -1,7 +1,7 @@
 import { createAuthClient } from "better-auth/react";
 
 export const authClient = createAuthClient({
-  baseURL: import.meta.env.VITE_API_URL ?? "",
+  baseURL: import.meta.env.VITE_API_URL || window.location.origin,
 });
 
 export const { signIn, signOut, useSession, changePassword } = authClient;