Hide system actor from user list and block show/edit

Index: filter out SystemActor.system_user_email() in query. Show/Form:
redirect to /users with flash when viewing or editing system actor user.
Index format_error: handle Ash errors without :message field.

lib/mv_web/live/user_live/form.ex

@@ -266,10 +266,31 @@ defmodule MvWeb.UserLive.Form do
 
     user =
       case params["id"] do
-        nil -> nil
-        id -> Ash.get!(Mv.Accounts.User, id, domain: Mv.Accounts, load: [:member], actor: actor)
+        nil ->
+          nil
+
+        id ->
+          loaded =
+            Ash.get!(Mv.Accounts.User, id, domain: Mv.Accounts, load: [:member], actor: actor)
+
+          if to_string(loaded.email) == Mv.Helpers.SystemActor.system_user_email() do
+            {:redirect, loaded}
+          else
+            loaded
+          end
       end
 
+    if match?({:redirect, _}, user) do
+      {:ok,
+       socket
+       |> put_flash(:error, gettext("This user cannot be edited."))
+       |> push_navigate(to: ~p"/users")}
+    else
+      mount_continue(user, params, socket)
+    end
+  end
+
+  defp mount_continue(user, params, socket) do
     action = if is_nil(user), do: gettext("New"), else: gettext("Edit")
     page_title = action <> " " <> gettext("User")