feat: Refactor backup and sync paths, enhance configuration flexibility

app/utils/backup.py

@@ -7,11 +7,17 @@ from app.utils.config import server_config
 from app.utils.local_playlist import load_local_playlist
 from app.utils.plex_client import plex_client
 
-# Default backup directory
-BACKUP_DIR = os.path.abspath(
+# Default backup directory (repo root /backups)
+DEFAULT_BACKUP_DIR = os.path.abspath(
     os.path.join(os.path.dirname(__file__), "..", "..", "backups")
 )
 
+# Allow Docker / users to relocate backups for centralized host backup.
+# Example: /app/data/backup
+BACKUP_DIR = os.path.abspath(
+    os.environ.get("PLEXPLAYLISTSYNC_BACKUP_DIR", DEFAULT_BACKUP_DIR)
+)
+
 
 def ensure_backup_dir():
     """Ensure the backup directory exists."""