Add WNTRMUTE issuing CA to system trust store

All NixOS machines now trust the Metacircular platform CA. This
allows curl, browsers, and Go services to verify TLS certificates
issued by Metacrypt without --insecure or custom CA flags.

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

configuration.nix

@@ -136,6 +136,9 @@
   };
   programs.ssh.askPassword =  "ksshaskpass";
 
+  # Trust the WNTRMUTE issuing CA for all Metacircular services.
+  security.pki.certificateFiles = [ ./certs/wntrmute-ca.pem ];
+
   nix.settings.experimental-features = [ "nix-command" "flakes" ];
   nix.settings.trusted-users = ["kyle"];