feat(scrobble): own timestamped play-log service (stats/Wrapped foundation)

Phase 1+2 of a self-hosted, multi-user listening archive — the basis for
day/month/year stats and a yearly "Wrapped". Runs IN ADDITION to the existing
Navidrome/Last.fm scrobble; never replaces it.

Service (isolated, own container):
- scrobble/scrobble-server.js — node:sqlite play-log (own volume), routes
  POST /scrobble/plays (idempotent by uuid), GET /scrobble/history (archive),
  DELETE /scrobble/plays?user= (test cleanup), GET /scrobble/health.
  Multi-user auth via Navidrome ping.view (cached) -> user not spoofable.
- docker-compose: novasonic-scrobble service (node:22, port 3710) + volume;
  backend bumped node:20->22 (EOL); SCROBBLE_URL plumbing (entrypoint, .env.example).

Capture (both platforms, offline-safe queue, idempotent batch flush):
- Fires at the existing scrobbleMode counted-play moment — consistent with
  Last.fm, respects the user's setting (no separate 50%/4min rule).
- Web: src/player/scrobbleLog.js (localStorage queue) + subsonicAuthParams()
  in api.js + hooks in player.js + flush init in main.js; S.cfg.scrobbleUrl.
- Android: data/PlayLogClient.kt (filesDir queue, reused Ktor client) +
  repo.logPlay/flushPlayLog + PlayerController hook + NovaSonicApp flush +
  scrobbleUrl in PrefsStore/SettingsViewModel/SettingsScreen (with test button).

Plan + design decisions documented in docs/scrobble-plan.md.

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

.env.example

@@ -3,6 +3,7 @@
 # Pre-fills the URLs on the setup screen
 NAVIDROME_URL=https://music.yourdomain.com
 BACKEND_URL=https://novasonic-api.yourdomain.com
+SCROBBLE_URL=https://novasonic-scrobble.yourdomain.com   # play-log / stats service (port 3710)
 
 # Absolute path to your Navidrome music library on the host
 MUSIC_PATH=/srv/navidrome/music