useApi: prefer BACKEND_URL, if provided

src/hooks/useApi.ts

@@ -1,6 +1,7 @@
 import { useMemo } from 'react';
 
 import { MastodonClient } from 'soapbox/api/MastodonClient';
+import * as BuildConfig from 'soapbox/build-config';
 
 import { useAppSelector } from './useAppSelector';
 import { useOwnAccount } from './useOwnAccount';
@@ -9,7 +10,7 @@ export function useApi(): MastodonClient {
   const { account } = useOwnAccount();
   const authUserUrl = useAppSelector((state) => state.auth.me);
   const accessToken = useAppSelector((state) => account ? state.auth.users.get(account.url)?.access_token : undefined);
-  const baseUrl = new URL(account?.url || authUserUrl || location.origin).origin;
+  const baseUrl = new URL(BuildConfig.BACKEND_URL || account?.url || authUserUrl || location.origin).origin;
 
   return useMemo(() => {
     return new MastodonClient(baseUrl, accessToken);