feat : Tag 모델 추가

app/Models/MainRequestFlow.php

@@ -2,7 +2,9 @@
 
 namespace App\Models;
 
-use Illuminate\Database\Eloquent\Model;
+use App\Models\MainRequest;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
 
 class MainRequestFlow extends Model
 {
@@ -26,7 +28,7 @@ class MainRequestFlow extends Model
     /**
      * 메인 업무 엔터티
      */
-    public function mainRequest()
+    public function mainRequest(): BelongsTo
     {
         return $this->belongsTo(MainRequest::class, 'main_request_id');
     }
@@ -34,7 +36,7 @@ public function mainRequest()
     /**
      * 폴리모픽 관계(견적, 주문, 발주 등)
      */
-    public function flowable()
+    public function flowable(): MorphTo
     {
         return $this->morphTo();
     }