list-editor: preserve aliases + description across URL edit

The url-edit modal's save handler was rebuilding state.music[idx]
from scratch using only meta-lookup fields, silently dropping aliases
and (newly added) description. Carry them over from prev so editing
a track's URL no longer wipes operator-entered metadata.

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

public/listEditor.js

@@ -396,7 +396,10 @@
         url: meta.url || url,
         title: meta.title || prev.title || '',
         artist: meta.channel || prev.artist || '',
-        durationSec: typeof meta.durationSec === 'number' ? meta.durationSec : (prev.durationSec || 0)
+        durationSec: typeof meta.durationSec === 'number' ? meta.durationSec : (prev.durationSec || 0),
+        // URL 만 바뀌었다고 운영자가 손으로 입력한 메타(별칭/설명)까지 날려선 안 된다.
+        aliases: Array.isArray(prev.aliases) ? prev.aliases : [],
+        description: typeof prev.description === 'string' ? prev.description : ''
       }
       markDirty()
       closeAllModals()