미리보기 기능 토글 적용

src/renderer/index.html

@@ -21,6 +21,8 @@
   </div>
   <div class="separator"></div>
   <button class="btn btn-success" id="btn-rename" disabled><span>✅</span>이름 변경 실행 (S)</button>
+  <div class="separator"></div>
+  <button class="btn btn-ghost active" id="btn-preview-toggle">🔍 미리보기</button>
   <div style="margin-left:auto; display:flex; align-items:center; gap:8px;">
     <span class="dir-path" id="dir-path">폴더를 선택하세요</span>
     <button class="btn btn-warning" id="btn-reveal" disabled>Finder에서 열기</button>