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)/settings.tsx

@@ -13,6 +13,7 @@ import {
   type NowPlayingProvider,
   type TrackSearchResultDTO,
 } from '@musicshare/shared';
+import { RelinkReminder } from '@/components/RelinkReminder';
 import { Screen } from '@/components/Screen';
 import { SharingControls } from '@/components/SharingControls';
 import { Body, Button, Card, Chip, Field, Heading, Row, Title } from '@/components/ui';
@@ -30,6 +31,7 @@ export default function SettingsScreen() {
       <Title>Settings</Title>
       <ProfileSection />
       <SharingControls />
+      <RelinkReminder />
       <PreferredService />
       <ThisPhone />
       <Connections />