feat: improve oidc only mode

lib/mv_web/live_helpers.ex

@@ -74,7 +74,7 @@ defmodule MvWeb.LiveHelpers do
 
         socket =
           socket
-          |> Phoenix.LiveView.put_flash(:error, "You don't have permission to access this page.")
+          |> maybe_put_access_denied_flash(user)
           |> Phoenix.LiveView.push_navigate(to: redirect_to)
 
         {:halt, socket}
@@ -82,6 +82,13 @@ defmodule MvWeb.LiveHelpers do
     end
   end
 
+  # Only show "no permission" when user is logged in; unauthenticated users are redirected to sign-in without flash.
+  defp maybe_put_access_denied_flash(socket, nil), do: socket
+
+  defp maybe_put_access_denied_flash(socket, _user) do
+    Phoenix.LiveView.put_flash(socket, :error, "You don't have permission to access this page.")
+  end
+
   defp ensure_user_role_loaded(socket) do
     user = socket.assigns[:current_user]