vault: add minimal vault config

hosts/vault01/configuration.nix

@@ -11,6 +11,7 @@
 
     ../../system
     ../../common/vm
+    ../../services/vault
   ];
 
   nixpkgs.config.allowUnfree = true;
@@ -58,4 +59,5 @@
   networking.firewall.enable = false;
 
   system.stateVersion = "25.11"; # Did you read the comment?
-}
+}
+

services/vault/default.nix

@@ -0,0 +1,8 @@
+{ ... }:
+{
+  services.vault = {
+    enable = true;
+
+    storageBackend = "file";
+  };
+}