feat: integrate latest HMDesign design system updates

.storybook/manager.css

@@ -102,6 +102,8 @@
 #storybook-sidebar-region [role='search'] > button:hover {
   background: rgba(0, 0, 0, .10);
 }
+/* Storybook's named creation action only; search/filter remain available. */
+#storybook-sidebar-region button[aria-label='Create a new story'] { display: none; }
 
 #storybook-explorer-tree .sidebar-subheading {
   position: relative;
@@ -141,8 +143,10 @@
   background: transparent;
   color: var(--color-fg-on-green-primary);
 }
+/* Manager-only expanded 2-depth branch face: Black 8%, independent of HM LNB CSS.
+   The separate Black 20% mapping remains reserved for the selected item's inset depth. */
 #storybook-explorer-tree .sidebar-item[data-hm-group='true'] {
-  background: var(--overlay-black-20);
+  background: rgba(0, 0, 0, .08);
   box-shadow: inset 1px 0 var(--hm-green-light-2);
 }
 #storybook-explorer-tree .sidebar-item[data-hm-group-start='true'] {