feat(search-by-product): extend order search to include product names

Added EXISTS subquery on order_items.original_name to the search filter
in OrdersRepository::buildPaginateFilters(). Users can now find orders
by typing a product name in the search field. Updated search placeholder
to reflect the new capability.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

resources/lang/pl.php

@@ -117,7 +117,7 @@ return [
             'source_updated_at' => 'Ostatnia zmiana',
         ],
         'filters' => [
-            'search' => 'Szukaj (numer, ID, login, email, klient)',
+            'search' => 'Szukaj (numer, klient, email, produkt)',
             'source' => 'Zrodlo',
             'status' => 'Status',
             'payment_status' => 'Platnosc',