OIDC: use UserHelpers.has_oidc? in index and show

- Index OIDC column and show OIDC item use has_oidc? instead of raw oidc_id.
- Avoids empty string showing as Linked.

lib/mv_web/live/user_live/index.html.heex

@@ -15,6 +15,8 @@
     rows={@users}
     row_id={fn user -> "row-#{user.id}" end}
     row_click={fn user -> JS.navigate(~p"/users/#{user}") end}
+    sort_field={@sort_field}
+    sort_order={@sort_order}
   >
     <:col
       :let={user}
@@ -45,6 +47,7 @@
     </:col>
     <:col
       :let={user}
+      sort_field={:email}
       label={
         sort_button(%{
           field: :email,
@@ -74,7 +77,7 @@
       <% end %>
     </:col>
     <:col :let={user} label={gettext("OIDC")}>
-      <%= if user.oidc_id do %>
+      <%= if MvWeb.Helpers.UserHelpers.has_oidc?(user) do %>
         <span>{gettext("Linked")}</span>
       <% else %>
         <span class="text-base-content/70">—</span>