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/services.ts

@@ -62,3 +62,35 @@ export function openUrl(
   if (direct) return { url: direct, exact: true };
   return { url: searchUrl(service, track.title, track.artist), exact: false };
 }
+
+/** Public profile page for scrobbling services (attribution links). */
+export function sourceProfileUrl(provider: string, username: string): string | null {
+  const u = encodeURIComponent(username);
+  if (provider === 'lastfm') return `https://www.last.fm/user/${u}`;
+  if (provider === 'listenbrainz') return `https://listenbrainz.org/user/${u}/`;
+  return null;
+}
+
+/** Where users re-link Spotify on each scrobbling service. */
+export const SPOTIFY_LINK_PAGES = {
+  lastfm: 'https://www.last.fm/settings/applications',
+  listenbrainz: 'https://listenbrainz.org/settings/music-services/details/',
+} as const;
+
+const QUIET_AFTER_MS = 7 * 86_400_000;
+
+/**
+ * A scrobbler that used to report plays but has gone silent for a week. Usually
+ * Spotify's link to it expired (Spotify makes users re-approve every 6 months).
+ */
+export function isQuietScrobbler(
+  c: { provider: string; status: string; lastActivityAt: string | null },
+  now = Date.now(),
+): c is { provider: 'lastfm' | 'listenbrainz'; status: string; lastActivityAt: string } {
+  return (
+    (c.provider === 'lastfm' || c.provider === 'listenbrainz') &&
+    c.status === 'active' &&
+    c.lastActivityAt !== null &&
+    now - new Date(c.lastActivityAt).getTime() > QUIET_AFTER_MS
+  );
+}