perf: remove images eager load from list and search endpoints

main_image_url is now stored directly on world_heritage_sites, so
thumbnail_url resolves from that column without touching world_heritage_site_images.

Loading the images relation on every list/search page was a redundant query
since the fallback to images[0].url is never reached for sites that have
main_image_url populated.

The detail endpoint (getHeritageById) retains its full images eager load
because it renders the complete image gallery.

Closes #465
Part of #463

Author: zigzagdev

src/app/Packages/Domains/WorldHeritageQueryService.php

@@ -58,9 +58,6 @@ public function getAllHeritages(
                         'countries.region',
                     ]);
                 },
-                'images' => static function ($imagesQuery): void {
-                    $imagesQuery->where('is_primary', true)->limit(1);
-                },
                 'descriptions' => static function ($descriptionsQuery): void {
                     $descriptionsQuery->select([
                         'world_heritage_descriptions.world_heritage_site_id',

src/app/Packages/Domains/WorldHeritageReadQueryService.php

@@ -41,9 +41,6 @@ public function findByIdsPreserveOrder(array $ids): Collection
                     $q->select('countries.state_party_code', 'countries.name_en', 'countries.name_jp', 'countries.region')
                         ->orderBy('countries.state_party_code', 'asc');
                 },
-                'images' => static function ($imageQuery): void {
-                    $imageQuery->where('is_primary', true)->limit(1);
-                },
                 'descriptions' => static function ($descriptionQuery): void {
                     $descriptionQuery->select([
                         'world_heritage_descriptions.world_heritage_site_id',