feat: SongCreator 씬 완성 — Beat Sage URL 지원, info.dat 메타데이터 자동 추출

- BeatSageUploader: audio_url 지원(UploadFromUrl), PollAndDownload 공통화, ZIP 500 오류 3회 재시도
- BeatSageConverter: info.dat 파싱(SongMetadata), BPM 자동 감지 → 노트 타이밍 변환에 적용
- SongCreatorManager: title/BPM 필수 입력 제거, 난이도 4개 자동 선택, GenerateFlowFromUrl 버그 수정
- NasPublisher: audioPath null 허용(URL 흐름에서 로컬 파일 없는 경우 스킵)
- .gitignore/.gitattributes 초기 설정

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Assets/VRBeatsKit/Scripts/Extension/GameObjectExtension.cs

@@ -0,0 +1,24 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace VRBeats
+{
+    public static class GameObjectExtension
+    {
+        /// <summary>
+        /// VR Shooter Kit extension method just try to get a component, if the component is no found we add one
+        /// </summary>       
+        public static T GetOrAddComponent<T>(this GameObject go) where T : Component
+        {
+            T component = go.GetComponent<T>();
+
+            if (component == null)
+                component = go.AddComponent<T>();
+
+            return component;
+        }
+    }
+
+}
+

Assets/VRBeatsKit/Scripts/Extension/GameObjectExtension.cs.meta

@@ -0,0 +1,18 @@
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+guid: 6da52cae31b2f74409182b3ba63cbf18
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
+AssetOrigin:
+  serializedVersion: 1
+  productId: 168243
+  packageName: VR Beats Kit
+  packageVersion: 2.0
+  assetPath: Assets/VRBeatsKit/Scripts/Extension/GameObjectExtension.cs
+  uploadId: 546658