feat(android): pinned similar artists tap through to library; note Following view idea

Pinned similar artists (Deezer related) were non-clickable on Android because
Deezer artists carry no Navidrome id. On tap, resolve the name against the
library (exact case-insensitive match) and navigate to that Navidrome artist if
present, else a short "not in your library" toast.

Also: extend the CHANGELOG "Artist following" backlog idea with a dedicated
"Following" view (grid of followed artists) + follow/unfollow toggle.

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

CHANGELOG.md

@@ -449,6 +449,7 @@ Primary causes identified:
   - 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).
+  - A **"Following" view** listing all artists you follow (grid of artist photos), as an entry point to their pages — a dedicated overview so you can see and manage who you follow, plus a follow/unfollow toggle on the artist page.
   - **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.