Create-account links for Last.fm and ListenBrainz, and Link Spotify for ListenBrainz

ListenBrainz accounts are MusicBrainz accounts, so its sign-up link goes to MusicBrainz.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mobile/src/components/setup/ServiceSignInSetup.tsx

@@ -1,8 +1,7 @@
 import { useState } from 'react';
-import { Linking } from 'react-native';
 import { mutate } from 'swr';
 import { SERVICE_LABELS } from '@musicshare/shared';
-import { SignInError, signInWithService } from '@/lib/connect';
+import { SignInError, openSignupPage, signInWithService } from '@/lib/connect';
 import { Button } from '../ui';
 import { ErrorText, SetupActions, SetupHeader, type SetupProps } from './common';
 
@@ -57,7 +56,7 @@ export function ServiceSignInSetup({
         />
         <ErrorText>{error}</ErrorText>
         <SetupActions primary="Sign in with Last.fm" loading={busy} onPrimary={run} onSkip={onDone} skipLabel={skipLabel} />
-        <Button small title="New to Last.fm? Create an account" onPress={() => Linking.openURL('https://www.last.fm/join')} />
+        <Button small title="New to Last.fm? Create an account" onPress={() => openSignupPage('lastfm')} />
       </>
     );
   }