fix:수당 없어도 1차/2차 수당현황 UI 표시

- calculateCommissionSummaryFromCollection()에서 빈 배열 체크 제거
- 수당 레코드가 없어도 0원으로 UI 표시

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Http/Controllers/Sales/SalesDashboardController.php

@@ -845,10 +845,6 @@ public function helpGuide(): View
      */
     private function calculateCommissionSummaryFromCollection($commissions): array
     {
-        if ($commissions->isEmpty()) {
-            return [];
-        }
-
         $thisMonth = now()->format('Y-m');
         $thisMonthStart = now()->startOfMonth()->format('Y-m-d');
         $thisMonthEnd = now()->endOfMonth()->format('Y-m-d');