sunken-ship: PurgeMissing = always (valid value; 'missing' was rejected by navidrome 0.61.2)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nixos/hosts/sunken-ship.nix

@@ -115,7 +115,10 @@
       # track IDs that Substreamer caches and then 500s on. Without
       # this, Navidrome keeps missing rows forever (default behaviour
       # preserves play history; we trade that for client-cache hygiene).
-      Scanner.PurgeMissing = "missing";
+      # Valid values: never | always | full. `always` purges on every
+      # scan (selective + full); risk on transient missing is fine
+      # here (stable local disk).
+      Scanner.PurgeMissing = "always";
     };
   };