Unlock everything, add a donation link, credit Last.fm, nudge re-linking

- Every feature is free for everyone (the plan system stays for later);
  remaining limits are abuse guards
- Optional website donation link (NEXT_PUBLIC_DONATION_URL). Not shown in
  the mobile apps, where tips to the developer generally need in-app
  purchase
- Last.fm/ListenBrainz-sourced plays link to the user's profile, as
  Last.fm's API terms require
- Connections track when they last saw activity; a scrobbler silent for
  over a week prompts re-linking Spotify (its link expires every 6 months)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/mobile/src/app/(tabs)/index.tsx

@@ -5,6 +5,7 @@ import { SafeAreaView } from 'react-native-safe-area-context';
 import useSWR from 'swr';
 import { sortFeed, type ConnectionDTO, type FeedItemDTO, type ProfileDTO } from '@musicshare/shared';
 import { NowPlayingCard } from '@/components/NowPlayingCard';
+import { RelinkReminder } from '@/components/RelinkReminder';
 import { SharingControls } from '@/components/SharingControls';
 import { Body, Button, Card, Title } from '@/components/ui';
 import { api } from '@/lib/api';
@@ -78,6 +79,7 @@ export default function FeedScreen() {
         ListHeaderComponent={
           <View style={styles.header}>
             <SharingControls compact />
+            <RelinkReminder />
             {offerAppleMusic && (
               <Card>
                 <Body>Connect Apple Music so friends see what you play. One tap.</Body>