feat: add csv export

lib/mv_web/live/member_live/index.ex

@@ -131,6 +131,7 @@ defmodule MvWeb.MemberLive.Index do
       )
       |> assign(:show_current_cycle, false)
       |> assign(:membership_fee_status_filter, nil)
+      |> assign_export_payload()
 
     # We call handle params to use the query from the URL
     {:ok, socket}
@@ -1729,5 +1730,36 @@ defmodule MvWeb.MemberLive.Index do
     |> assign(:selected_count, selected_count)
     |> assign(:any_selected?, any_selected?)
     |> assign(:mailto_bcc, mailto_bcc)
+    |> assign_export_payload()
   end
+
+  # Builds the export payload map and assigns :export_payload_json for the CSV export form.
+  # Called when selection, visible fields, query, or sort change so the form always has current data.
+  defp assign_export_payload(socket) do
+    payload = build_export_payload(socket)
+    assign(socket, :export_payload_json, Jason.encode!(payload))
+  end
+
+  defp build_export_payload(socket) do
+    member_fields_visible = socket.assigns[:member_fields_visible] || []
+    visible_custom_field_ids = socket.assigns[:visible_custom_field_ids] || []
+
+    %{
+      selected_ids: socket.assigns.selected_members |> MapSet.to_list(),
+      member_fields: Enum.map(member_fields_visible, &Atom.to_string/1),
+      custom_field_ids: visible_custom_field_ids,
+      query: socket.assigns[:query] || nil,
+      sort_field: export_sort_field(socket.assigns[:sort_field]),
+      sort_order: export_sort_order(socket.assigns[:sort_order])
+    }
+  end
+
+  defp export_sort_field(nil), do: nil
+  defp export_sort_field(f) when is_atom(f), do: Atom.to_string(f)
+  defp export_sort_field(f) when is_binary(f), do: f
+
+  defp export_sort_order(nil), do: nil
+  defp export_sort_order(:asc), do: "asc"
+  defp export_sort_order(:desc), do: "desc"
+  defp export_sort_order(o) when is_binary(o), do: o
 end