Add getRegionCount to WorldHeritageQueryService Acceptance Criteria

[zigzagdev]

Acceptance Criteria

• WorldHeritageQueryService has a getRegionCount method
• Returns a grouped count of heritage sites by study_region

Tasks

• Add getRegionCount(): array to WorldHeritageQueryService
• Group and count records by study_region from the WorldHeritage model

public function getRegionCount(): array
{
    return WorldHeritage::query()
        ->whereNotNull('study_region')
        ->groupBy('study_region')
        ->selectRaw('study_region, COUNT(*) as count')
        ->pluck('count', 'study_region')
        ->toArray();
}