feat: 신규거래처 알림 메시지 간소화 및 신용평가 모달 경로 수정

- 알림 메시지: "신규 거래처 :name 등록 완료" → ":name 등록"
- 모달 파라미터: openModal=credit → modal=credit

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

app/Services/TodayIssueObserverService.php

@@ -249,7 +249,7 @@ public function handleClientCreated(Client $client): void
             content: __('message.today_issue.new_client', [
                 'name' => $client->name,
             ]),
-            path: "/accounting/vendors/{$client->id}?openModal=credit",
+            path: "/accounting/vendors/{$client->id}?modal=credit",
             needsApproval: false,
             expiresAt: Carbon::now()->addDays(7)
         );