fix(org-chart): separate fixed and expanded canvas backgrounds

packages/org-chart/src/styles/org-chart-expanded.css

@@ -27,7 +27,9 @@
   overflow: hidden;
   touch-action: none;
   cursor: grab;
-  background: var(--hm-orgchart-resolved-bg-surface);
+  /* Canvas input is independent of cards and the outer preview frame.
+     Keep existing bg-surface themes as the fallback (standalone: #ffffff). */
+  background: var(--hm-orgchart-expanded-canvas-background, var(--hm-orgchart-resolved-bg-surface));
 }
 .hm-orgchart-expanded .hm-orgchart-forest {
   position: absolute;