fix: prevent spurious y-scrollbar when section has overflow-x: auto on mobile

Setting overflow-x: auto forces overflow-y off 'visible' per CSS spec,
which caused an unwanted vertical scrollbar in stacked note sections.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/StackedNote.vue

@@ -278,6 +278,7 @@ $border-color: rgba(18, 19, 58, 0.2);
     section {
       padding: 1rem 0 2rem;
       overflow-x: auto;
+      overflow-y: hidden;
     }
 
     .note-content {