feat: [현황판/악성채권] 카드별 sub_label(대표 거래처명 + 건수) 추가

- BadDebtService: summary에 카드별(전체/추심중/법적조치/회수완료) sub_labels 추가
- StatusBoardService: 악성채권·신규거래처·결재 카드에 sub_label 추가
  - 악성채권: 최다 금액 거래처명
  - 신규거래처: 최근 등록 업체명
  - 결재: 최근 결재 제목

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Services/BadDebtService.php

@@ -110,6 +110,9 @@ public function summary(array $params = []): array
             ->distinct('client_id')
             ->count('client_id');
 
+        // per-card sub_label: 각 상태별 최다 금액 거래처명 + 건수
+        $subLabels = $this->buildPerCardSubLabels($query);
+
         return [
             'total_amount' => (float) $totalAmount,
             'collecting_amount' => (float) $collectingAmount,
@@ -117,9 +120,56 @@ public function summary(array $params = []): array
             'recovered_amount' => (float) $recoveredAmount,
             'bad_debt_amount' => (float) $badDebtAmount,
             'client_count' => $clientCount,
+            'sub_labels' => $subLabels,
         ];
     }
 
+    /**
+     * 카드별 sub_label 생성 (최다 금액 거래처명 + 건수)
+     */
+    private function buildPerCardSubLabels($baseQuery): array
+    {
+        $result = [];
+        $statusScopes = [
+            'dc1' => null,           // 전체 (누적)
+            'dc2' => 'collecting',   // 추심중
+            'dc3' => 'legalAction',  // 법적조치
+            'dc4' => 'recovered',    // 회수완료
+        ];
+
+        foreach ($statusScopes as $cardId => $scope) {
+            $q = clone $baseQuery;
+            if ($scope) {
+                $q = $q->$scope();
+            }
+
+            $clientCount = (clone $q)->distinct('client_id')->count('client_id');
+
+            if ($clientCount <= 0) {
+                $result[$cardId] = null;
+
+                continue;
+            }
+
+            $topClient = (clone $q)
+                ->join('clients', 'bad_debts.client_id', '=', 'clients.id')
+                ->selectRaw('clients.name, SUM(bad_debts.debt_amount) as total_amount')
+                ->groupBy('clients.id', 'clients.name')
+                ->orderByDesc('total_amount')
+                ->first();
+
+            if ($topClient) {
+                $result[$cardId] = $clientCount > 1
+                    ? $topClient->name.' 외 '.($clientCount - 1).'건'
+                    : $topClient->name;
+            } else {
+                $result[$cardId] = null;
+            }
+        }
+
+        return $result;
+    }
+
     /**
      * 악성채권 상세 조회
      */