ML-168: broadcast index_changed event after background import

Import workers now broadcast :records_index_changed on
"records:index_changed" after successful import via
Records.broadcast_index_changed/0.

CollectionLive.Index and WishlistLive.Index subscribe to the
topic in mount/3 and reload their record streams on receipt,
with a live_action guard to skip reloads when the grid is
hidden behind a modal (:import, :barcode_scan).

IndexActions.handle_index_changed/1 refreshes total_entries
before reloading to keep the pagination bar accurate.

lib/music_library_web/live_helpers/index_actions.ex

@@ -146,6 +146,18 @@ defmodule MusicLibraryWeb.LiveHelpers.IndexActions do
     {:noreply, load_and_assign_records(socket, socket.assigns.record_list_params)}
   end
 
+  @doc """
+  Handles a PubSub notification that records have changed.
+  Refreshes total_entries and reloads the record stream using the current parameters.
+  """
+  def handle_index_changed(socket) do
+    config = socket.assigns.index_config
+    params = socket.assigns.record_list_params
+    total_records = config.context_module.search_records_count(params.query)
+    updated_params = %{params | total_entries: total_records}
+    load_and_assign_records(socket, updated_params)
+  end
+
   defp record_page_title(record, config) do
     Enum.join(
       [