list-editor: add per-track description button + modal

Each music list row now shows a 설명 button immediately to the left of
the 별칭 button. Click opens a modal with a multi-line textarea; on
close the value is persisted into MusicListEntry.description and saved
to the same pack list JSON. The button gets a hasDesc visual indicator
when filled. Description is stored but intentionally not consumed by
datapack export or alias matching — purely informational metadata.

- types.ts: add description: string to MusicListEntry
- store.ts: normalize entry.description via sanitizeStr (defaults to '')
- listEditor.ejs: new #descModal alongside aliasModal
- listEditor.js: render descBtn left of aliasBtn, attach handlers,
  also set description: '' on playlist-fetched entries
- styles.css: extend trackRow grid to 6 cols, reuse aliasBtn styling
  for descBtn, add descTextarea sizing
- locale (ko-kr): descBtn / descModalTitle / descBack / descPlaceholder
  / descHint

Backwards-compatible: existing list JSON files without description
field normalize to ''.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

public/listEditor.js

@@ -103,6 +103,7 @@
       var aliasLabel = aliasCount > 0
         ? tt('aliasBtnWithCount', { count: aliasCount })
         : tt('aliasBtn')
+      var hasDesc = typeof entry.description === 'string' && entry.description.trim().length > 0
       li.innerHTML =
         '<span class="rowNum">' + (idx + 1) + '</span>' +
         '<img class="rowThumb" src="' + thumbUrl(entry.url) + '" alt="" loading="lazy" draggable="false"/>' +
@@ -114,12 +115,16 @@
             escapeHtml(entry.artist || '') +
           '</div>' +
         '</div>' +
+        '<button type="button" class="descBtn' + (hasDesc ? ' hasDesc' : '') + '" data-desc-open="' + idx + '" draggable="false">' +
+          escapeHtml(tt('descBtn')) +
+        '</button>' +
         '<button type="button" class="aliasBtn' + (aliasCount > 0 ? ' hasAliases' : '') + '" data-alias-open="' + idx + '" draggable="false">' +
           escapeHtml(aliasLabel) +
         '</button>' +
         '<span class="rowDur">' + fmtTime(entry.durationSec) + '</span>'
       attachDraggable(li, 'music', idx)
       attachInlineEdit(li, idx)
+      attachDescBtn(li, idx)
       attachAliasBtn(li, idx)
       ol.appendChild(li)
     })
@@ -527,6 +532,57 @@
     if (e.target === aliasModal) closeAliasModalSaving()
   })
 
+  // ── 설명 모달 (음악) ─────────────────────────────────
+  // 별칭 모달과 같은 패턴: 모달 닫힐 때 textarea 값을 state.music[idx].description 에 저장.
+  var descModal = document.getElementById('descModal')
+  var descTextarea = document.getElementById('desc-textarea')
+  var descModalTitleEl = document.getElementById('desc-modal-title')
+  var descBackBtn = document.getElementById('desc-back')
+  var descEditingIdx = -1
+
+  function attachDescBtn(li, idx) {
+    var btn = li.querySelector('[data-desc-open]')
+    if (!btn) return
+    btn.addEventListener('mousedown', function (e) { e.stopPropagation() })
+    btn.addEventListener('click', function (e) {
+      e.stopPropagation()
+      openDescModal(idx)
+    })
+  }
+
+  function openDescModal(idx) {
+    if (!state.music[idx]) return
+    descEditingIdx = idx
+    var entry = state.music[idx]
+    descModalTitleEl.textContent = tt('descModalTitle', { title: entry.title || tt('titleFallback') })
+    descTextarea.value = typeof entry.description === 'string' ? entry.description : ''
+    descModal.hidden = false
+    setTimeout(function () { descTextarea.focus() }, 0)
+  }
+
+  function closeDescModalSaving() {
+    if (descEditingIdx < 0 || !state.music[descEditingIdx]) {
+      descModal.hidden = true
+      descEditingIdx = -1
+      return
+    }
+    // textarea 값을 그대로 저장하되, 줄바꿈은 보존하고 양끝 공백만 다듬는다.
+    var nextDesc = (descTextarea.value || '').replace(/\r\n/g, '\n').trim()
+    var prev = state.music[descEditingIdx].description || ''
+    if (nextDesc !== prev) {
+      state.music[descEditingIdx].description = nextDesc
+      markDirty()
+      renderMusic()
+    }
+    descModal.hidden = true
+    descEditingIdx = -1
+  }
+
+  descBackBtn.addEventListener('click', closeDescModalSaving)
+  descModal.addEventListener('click', function (e) {
+    if (e.target === descModal) closeDescModalSaving()
+  })
+
   // ── 사진목록: 음악목록 그대로 복사 ─────────────────
   document.getElementById('image-from-music').addEventListener('click', function () {
     if (state.music.length === 0) {
@@ -637,7 +693,7 @@
         var entries = result.body.entries || []
         if (target === 'music') {
           state.music = entries.map(function (e) {
-            return { url: e.url, title: e.title || '', artist: e.channel || '', durationSec: e.durationSec || 0 }
+            return { url: e.url, title: e.title || '', artist: e.channel || '', durationSec: e.durationSec || 0, aliases: [], description: '' }
           })
           renderMusic()
         } else {

public/styles.css

@@ -407,19 +407,24 @@ body.siteBody.centerLayout {
 .trackList { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 4px; }
 .trackRow {
   display: grid;
-  grid-template-columns: 36px 80px 1fr auto auto;
+  grid-template-columns: 36px 80px 1fr auto auto auto;
   gap: 12px; align-items: center;
   padding: 8px 12px; background: var(--bg-card);
   border: 1px solid var(--border); border-radius: 8px;
   cursor: grab; user-select: none;
 }
-.aliasBtn {
+.aliasBtn, .descBtn {
   background: var(--bg); border: 1px solid var(--border); color: var(--text);
   padding: 6px 10px; border-radius: 6px; cursor: pointer; font-size: 12px;
   white-space: nowrap;
 }
-.aliasBtn:hover { border-color: var(--accent); }
-.aliasBtn.hasAliases { border-color: var(--accent); color: var(--accent); }
+.aliasBtn:hover, .descBtn:hover { border-color: var(--accent); }
+.aliasBtn.hasAliases, .descBtn.hasDesc { border-color: var(--accent); color: var(--accent); }
+.descTextarea {
+  width: 100%; min-height: 140px; resize: vertical;
+  font-family: inherit; font-size: 13px; line-height: 1.5;
+  padding: 8px 10px;
+}
 
 /* 별칭 모달 */
 .aliasModalHeader {