feat: add cache-only storage mode for streaming without library persistence

.env.example

@@ -1,7 +1,7 @@
 # Navidrome/Subsonic server URL
 SUBSONIC_URL=http://localhost:4533
 
-# Path where downloaded songs will be stored on the host
+# Path where downloaded songs will be stored on the host (only applies if STORAGE_MODE=Permanent)
 DOWNLOAD_PATH=./downloads
 
 # Music service to use: Deezer or Qobuz (default: Deezer)
@@ -46,3 +46,15 @@ EXPLICIT_FILTER=All
 # - Album: When playing a track, download the entire album in background
 #          The played track is downloaded first, remaining tracks are queued
 DOWNLOAD_MODE=Track
+
+# Storage mode (optional, default: Permanent)
+# - Permanent: Files are saved to the library permanently and registered in Navidrome
+# - Cache: Files are stored in /tmp and automatically cleaned up after CACHE_DURATION_HOURS
+#          Not registered in Navidrome, ideal for streaming without library bloat
+STORAGE_MODE=Permanent
+
+# Cache duration in hours (optional, default: 1)
+# Files older than this duration will be automatically deleted when STORAGE_MODE=Cache
+# Based on last access time (updated each time the file is streamed)
+# Cache location: /tmp/octo-fiesta-cache (automatic, no configuration needed)
+CACHE_DURATION_HOURS=1