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.ts

@@ -36,6 +36,8 @@ export interface NowPlayingDTO {
   source: NowPlayingProvider;
   /** The app it's playing in, when a phone reported it (e.g. "Spotify"). */
   sourceApp: string | null;
+  /** Link to the source for attribution, e.g. the user's Last.fm profile (required by Last.fm's terms). */
+  sourceUrl: string | null;
   progressMs: number | null;
   updatedAt: string;
 }
@@ -79,6 +81,8 @@ export interface ProfileDTO {
   nowPlaying: NowPlayingDTO | null;
   /** Most recent first, not including the track playing right now. */
   recent: RecentPlayDTO[];
+  /** Profile links for sources whose data appears here (Last.fm requires attribution). */
+  attribution: Partial<Record<'lastfm' | 'listenbrainz', string>>;
 }
 
 export interface ConnectionDTO {
@@ -88,6 +92,8 @@ export interface ConnectionDTO {
   status: 'active' | 'error';
   lastError: string | null;
   lastPolledAt: string | null;
+  /** Last time this connection saw something playing. */
+  lastActivityAt: string | null;
   /** Secret URL the user can paste into Plex/Jellyfin for instant updates. */
   webhookUrl: string | null;
 }