feat: add Ampache music streaming server to media stack

- Add ampache service to media/compose.yaml with PostgreSQL backend
- Create ampache database in postgres init script
- Configure Ampache environment variables in arty.yml
- Mount Music directory read-only
- Expose at ampache.media.pivoine.art via Traefik

arty.yml

@@ -161,6 +161,9 @@ envs:
     MEDIA_KOEL_DEBUG: false
     MEDIA_KOEL_MEMORY_LIMIT: 512
     MEDIA_KOEL_STREAMING_METHOD: x-sendfile
+    MEDIA_AMPACHE_IMAGE: ampache/ampache:latest
+    MEDIA_AMPACHE_TRAEFIK_HOST: ampache.media.pivoine.art
+    MEDIA_AMPACHE_DB_NAME: ampache
     # PairDrop
     DROP_TRAEFIK_ENABLED: true
     DROP_COMPOSE_PROJECT_NAME: drop