docs: plan artist following + new-release/concert notifications

Follow artists and get notified on new releases (iTunes/MusicBrainz/Last.fm)
and nearby concerts (reusing the existing Ticketmaster integration), surfaced
in the in-app notification bell, with a download action from the alert.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -308,6 +308,11 @@ Primary causes identified:
   - **Keep what you like:** per-track (or whole-mix) option to **promote into the permanent library** instead of letting it expire.
   - Goal: completely random/unfamiliar music you don't already know — like Spotify's curated/discovery playlists, but self-hosted.
   - Open questions: where downloaded-but-temporary tracks live vs. the main library (separate folder + retention job), how Navidrome should/shouldn't index them, and dedupe against tracks you already own.
+- **Web + Android** — **Artist following + new-release & concert notifications** — follow artists and get notified when they drop something new or play nearby. Idea:
+  - A **follow list** of artists (stored per user, e.g. in app settings / a small backend table).
+  - **New-release alerts:** periodic check for new albums/singles by followed artists (sources: iTunes lookup / MusicBrainz / Last.fm), surfaced in the existing in-app notification bell (and optionally push).
+  - **Concert alerts:** reuse the existing **Ticketmaster** events integration to notify when a followed artist has nearby/upcoming shows.
+  - Ties into the importer: a "download this new release" action straight from the notification.
 - **Android** — Playlist drag-and-drop / sort order
 - **Android** — Artist page iTunes fallback (for artists not in Navidrome)
 - **Android** — Romaji / Japanese sort support