fix(sunken-ship): set fsType=none on /srv/music bind mount

nixos-rebuild was failing with "fsType accessed but has no value
defined" on newer nixpkgs. Bind mounts need fsType=none explicitly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nixos/hosts/sunken-ship.nix

@@ -95,6 +95,7 @@ in
   # Persist the bind mount so navidrome can read music outside ProtectHome.
   fileSystems."/srv/music" = {
     device = "/home/danny/music";
+    fsType = "none";
     options = [ "bind" "ro" ];
   };