feat: item_fields에 field_key, is_locked 컬럼 추가

- field_key: {ID}_{key} 형식으로 고유키 생성
- is_locked, locked_by, locked_at 잠금 컬럼 추가
- ItemFieldService: store/update/clone 로직 수정
- FormRequest: field_key 검증 규칙 추가
- Swagger 스키마 업데이트

app/Http/Requests/ItemMaster/ItemFieldStoreRequest.php

@@ -16,6 +16,7 @@ public function rules(): array
         return [
             'group_id' => 'nullable|integer|min:1', // 계층번호
             'field_name' => 'required|string|max:255',
+            'field_key' => 'nullable|string|max:80|regex:/^[a-zA-Z][a-zA-Z0-9_]*$/',
             'field_type' => 'required|in:textbox,number,dropdown,checkbox,date,textarea',
             'is_required' => 'nullable|boolean',
             'default_value' => 'nullable|string',
@@ -24,6 +25,14 @@ public function rules(): array
             'validation_rules' => 'nullable|array',
             'options' => 'nullable|array',
             'properties' => 'nullable|array',
+            'is_locked' => 'nullable|boolean',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'field_key.regex' => __('validation.field_key_format'),
         ];
     }
 }