feat(playlist): import UI with drag reorder + random/sequential ID toggle (STEP 5)

Adds /op/folder/:top/:sub/playlist/new page that lets the operator paste a
YouTube playlist URL, probe entries via yt-dlp, reorder them by drag, edit
title/ID per row, and choose between random IDs or zero-padded sequential
IDs before registering all jobs in one batch.

src/routes/op.ts

@@ -218,6 +218,34 @@ opRouter.get(
   }
 )
 
+// ─── 플레이리스트 import 페이지 ─────────────────────────────────────────
+
+opRouter.get(
+  '/op/folder/:topName/:subName/playlist/new',
+  requireAuth,
+  (req, res, next) => {
+    try {
+      const segments = collectFolderSegments(req.params)
+      const folder = getFolderByPath(segments)
+      if (!folder) {
+        res.status(404).send('폴더를 찾을 수 없습니다.')
+        return
+      }
+      if (folder.parentId === null) {
+        res.status(400).send('플레이리스트는 하위 폴더에서만 등록할 수 있습니다.')
+        return
+      }
+      res.render('op/playlist', {
+        userId: req.session.userId,
+        folder,
+        breadcrumb: folderPathNames(folder.id)
+      })
+    } catch (err) {
+      next(err)
+    }
+  }
+)
+
 // ─── 영상 업로드 / 유튜브 ───────────────────────────────────────────────
 
 function uploadSingle(fieldName: string) {