Storyline: hide the chapter-pane scrollbar (scrolling still works)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

assets/styles/app.css

@@ -460,6 +460,12 @@ table.dataTable {
     overflow-y: auto;
     overflow-x: hidden;
     padding-bottom: 1.5rem;
+    /* Scroll stays available; the bar is just hidden. */
+    scrollbar-width: none;          /* Firefox */
+    -ms-overflow-style: none;       /* legacy Edge */
+}
+.storyline-split-main::-webkit-scrollbar {
+    display: none;                  /* Chrome, Safari, Edge */
 }
 .storyline-notes-resize {
     flex: 0 0 auto;