Show * mark when list editor has unsaved changes

Add a red asterisk in the top-right of the dashboard header (and
prefix the document title with *) whenever the dirty flag is set,
so the user can tell at a glance that the music/image list hasn't
been saved yet. The indicator is driven by markDirty/markClean so
it follows the existing tracking.

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

views/op/listEditor.ejs

@@ -16,6 +16,7 @@
         <h1 style="margin-top:20px;"><%= pack.name %></h1>
         <p class="muted"><%= packKey %>.json</p>
       </div>
+      <div class="dirtyMark" id="dirty-mark" hidden title="저장되지 않은 변경사항이 있습니다">*</div>
     </section>
 
     <div class="tabBar">