Fix Kingfisher container: add bash and coreutils for CronJob shell

Nix containers don't include a shell by default. The CronJob needs
/bin/bash for the inline script that generates timestamped filenames.

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

containers/kingfisher/default.nix

@@ -98,6 +98,8 @@ pkgs.dockerTools.buildLayeredImage {
   name = "blumeops/kingfisher";
   contents = [
     kingfisher
+    pkgs.bashInteractive
+    pkgs.coreutils
     pkgs.cacert
     pkgs.git
     pkgs.tzdata