feat : Tag 모델 추가

app/Models/MainRequest.php

@@ -3,6 +3,7 @@
 namespace App\Models;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\SoftDeletes;
 
 class MainRequest extends Model
@@ -28,7 +29,7 @@ class MainRequest extends Model
     /**
      * 전체 이력(흐름) 리스트
      */
-    public function flows()
+    public function flows(): HasMany
     {
         return $this->hasMany(MainRequestFlow::class, 'main_request_id');
     }