feat: add user count display for each role

- Add Users column showing number of users assigned to each role
- Load user counts efficiently in single query to avoid N+1
- Similar implementation to membership fee types member count

lib/mv_web/live/role_live/index.ex

@@ -17,16 +17,21 @@ defmodule MvWeb.RoleLive.Index do
   use MvWeb, :live_view
 
   alias Mv.Authorization
+  alias Mv.Accounts
+
+  require Ash.Query
 
   @impl true
   def mount(_params, _session, socket) do
     socket = ensure_user_role_loaded(socket)
     roles = load_roles()
+    user_counts = load_user_counts(roles)
 
     {:ok,
      socket
      |> assign(:page_title, gettext("Listing Roles"))
-     |> assign(:roles, roles)}
+     |> assign(:roles, roles)
+     |> assign(:user_counts, user_counts)}
   end
 
   defp ensure_user_role_loaded(socket) do
@@ -86,6 +91,29 @@ defmodule MvWeb.RoleLive.Index do
     end
   end
 
+  # Loads all user counts for roles in a single query to avoid N+1 queries
+  defp load_user_counts(roles) do
+    role_ids = Enum.map(roles, & &1.id)
+
+    # Load all users with role_id in a single query
+    users =
+      Accounts.User
+      |> Ash.Query.filter(role_id in ^role_ids)
+      |> Ash.Query.select([:role_id])
+      |> Ash.read!(domain: Mv.Accounts)
+
+    # Group by role_id and count
+    users
+    |> Enum.group_by(& &1.role_id)
+    |> Enum.map(fn {role_id, users_list} -> {role_id, length(users_list)} end)
+    |> Map.new()
+  end
+
+  # Gets user count from preloaded assigns map
+  defp get_user_count(role, user_counts) do
+    Map.get(user_counts, role.id, 0)
+  end
+
   defp format_error(%Ash.Error.Invalid{} = error) do
     Enum.map_join(error.errors, ", ", fn e -> e.message end)
   end