fix: [payroll] tenant_id null 오류 수정

- session('selected_tenant_id')에 기본값 1 추가
- PayrollSetting::getOrCreate, scopeForTenant 수정
- PayrollService 전체 tenant_id 조회에 기본값 적용
- Payroll 모델 scopeForTenant 동일 패턴 적용

app/Models/HR/PayrollSetting.php

@@ -62,7 +62,7 @@ class PayrollSetting extends Model
 
     public function scopeForTenant($query, ?int $tenantId = null)
     {
-        $tenantId = $tenantId ?? session('selected_tenant_id') ?? 1;
+        $tenantId = $tenantId ?? session('selected_tenant_id', 1);
 
         return $query->where('tenant_id', $tenantId);
     }
@@ -73,7 +73,7 @@ public function scopeForTenant($query, ?int $tenantId = null)
 
     public static function getOrCreate(?int $tenantId = null): self
     {
-        $tenantId = $tenantId ?? session('selected_tenant_id') ?? 1;
+        $tenantId = $tenantId ?? session('selected_tenant_id', 1);
 
         return self::firstOrCreate(
             ['tenant_id' => $tenantId],