perf: optimize member index selection calculations

Calculate selected_count, any_selected? and mailto_bcc once in assigns
instead of recalculating Enum.any? and Enum.count multiple times in template.
This improves render performance and makes the template code more readable.

lib/mv_web/live/member_live/index.ex

@@ -145,7 +145,10 @@ defmodule MvWeb.MemberLive.Index do
         MapSet.put(socket.assigns.selected_members, id)
       end
 
-    {:noreply, assign(socket, :selected_members, selected)}
+    {:noreply,
+     socket
+     |> assign(:selected_members, selected)
+     |> update_selection_assigns()}
   end
 
   @impl true
@@ -159,7 +162,10 @@ defmodule MvWeb.MemberLive.Index do
         all_ids
       end
 
-    {:noreply, assign(socket, :selected_members, selected)}
+    {:noreply,
+     socket
+     |> assign(:selected_members, selected)
+     |> update_selection_assigns()}
   end
 
   @impl true
@@ -238,6 +244,7 @@ defmodule MvWeb.MemberLive.Index do
       socket
       |> assign(:query, q)
       |> load_members()
+      |> update_selection_assigns()
 
     existing_field_query = socket.assigns.sort_field
     existing_sort_query = socket.assigns.sort_order
@@ -263,6 +270,7 @@ defmodule MvWeb.MemberLive.Index do
       socket
       |> assign(:paid_filter, filter)
       |> load_members()
+      |> update_selection_assigns()
 
     # Build the URL with all params including new filter
     query_params =
@@ -309,6 +317,7 @@ defmodule MvWeb.MemberLive.Index do
       |> assign(:visible_custom_field_ids, extract_custom_field_ids(visible_custom_fields))
       |> load_members()
       |> prepare_dynamic_cols()
+      |> update_selection_assigns()
       |> push_field_selection_url()
 
     {:noreply, socket}
@@ -338,6 +347,7 @@ defmodule MvWeb.MemberLive.Index do
       |> assign(:visible_custom_field_ids, extract_custom_field_ids(visible_custom_fields))
       |> load_members()
       |> prepare_dynamic_cols()
+      |> update_selection_assigns()
       |> push_field_selection_url()
 
     {:noreply, socket}
@@ -389,6 +399,7 @@ defmodule MvWeb.MemberLive.Index do
       |> assign(:visible_custom_field_ids, extract_custom_field_ids(visible_custom_fields))
       |> load_members()
       |> prepare_dynamic_cols()
+      |> update_selection_assigns()
 
     {:noreply, socket}
   end
@@ -1112,4 +1123,30 @@ defmodule MvWeb.MemberLive.Index do
 
   # Public helper function to format dates for use in templates
   def format_date(date), do: DateFormatter.format_date(date)
+
+  # Updates selection-related assigns (selected_count, any_selected?, mailto_bcc)
+  # to avoid recalculating Enum.any? and Enum.count multiple times in templates.
+  defp update_selection_assigns(socket) do
+    members = socket.assigns.members
+    selected_members = socket.assigns.selected_members
+
+    selected_count =
+      Enum.count(members, &MapSet.member?(selected_members, &1.id))
+
+    any_selected? =
+      Enum.any?(members, &MapSet.member?(selected_members, &1.id))
+
+    mailto_bcc =
+      if any_selected? do
+        format_selected_member_emails(members, selected_members)
+        |> Enum.join(", ")
+      else
+        ""
+      end
+
+    socket
+    |> assign(:selected_count, selected_count)
+    |> assign(:any_selected?, any_selected?)
+    |> assign(:mailto_bcc, mailto_bcc)
+  end
 end