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

packages/shared/src/dto.test.ts

@@ -8,6 +8,7 @@ function item(username: string, opts: { pinnedAt?: string; isPlaying?: boolean;
     isPlaying: opts.isPlaying ?? false,
     source: 'spotify',
     sourceApp: null,
+    sourceUrl: null,
     progressMs: null,
     updatedAt: opts.updatedAt ?? '2026-01-01T00:00:00.000Z',
     pinnedAt: opts.pinnedAt ?? null,