fix: [esign] MNG EsignSigner 모델에 역할/상태 상수 추가

- ROLE_CREATOR, ROLE_COUNTERPART 상수 추가
- STATUS_WAITING~STATUS_REJECTED 상수 추가
- 운영서버 Undefined constant 오류 수정

app/Models/ESign/EsignSigner.php

@@ -10,6 +10,22 @@ class EsignSigner extends Model
 {
     protected $table = 'esign_signers';
 
+    // 역할 상수
+    public const ROLE_CREATOR = 'creator';
+
+    public const ROLE_COUNTERPART = 'counterpart';
+
+    // 상태 상수
+    public const STATUS_WAITING = 'waiting';
+
+    public const STATUS_NOTIFIED = 'notified';
+
+    public const STATUS_AUTHENTICATED = 'authenticated';
+
+    public const STATUS_SIGNED = 'signed';
+
+    public const STATUS_REJECTED = 'rejected';
+
     protected $fillable = [
         'tenant_id',
         'contract_id',