style: 문의사항 '답변 완료' 배지 색상 회색으로 통일

목록형(index)의 '답변 완료' 배지를 teal → gray로 변경해 전체보기(all)와 통일.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/Views/admin/feedback/index.php

@@ -12,7 +12,7 @@ $badge = static function (string $s): string {
     $map = [
         'new'         => 'bg-blue-50 text-blue-700',
         'in_progress' => 'bg-amber-50 text-amber-700',
-        'answered'    => 'bg-teal-50 text-teal-700',
+        'answered'    => 'bg-gray-100 text-gray-500',
         'done'        => 'bg-emerald-50 text-emerald-700',
         'hold'        => 'bg-gray-100 text-gray-500',
     ];