fix: remove owner/group from attic-credentials secret

atticd uses DynamicUser so the atticd user doesn't exist during
activation when agenix decrypts secrets. Default to root:root —
systemd reads the EnvironmentFile as root before dropping privileges.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: stackptr

hosts/glyph/services/attic.nix

@@ -1,10 +1,5 @@
 {config, ...}: {
-  age.secrets.attic-credentials = {
-    file = ./../secrets/attic-credentials.age;
-    mode = "440";
-    owner = "atticd";
-    group = "atticd";
-  };
+  age.secrets.attic-credentials.file = ./../secrets/attic-credentials.age;
 
   systemd.services.atticd = {
     after = ["postgresql.service"];