fix(ui): use tokens for button loading state (#40884)

Author: arvsrn

packages/ui/src/v2/components/button-v2.css

@@ -195,9 +195,9 @@
 
 /* Loading */
 [data-component="button-v2"][data-variant="loading"] {
-  background: #f2f2f2;
+  background: var(--v2-background-bg-layer-02);
   color: var(--v2-text-text-base);
-  box-shadow: inset 0 0 0 0.5px rgba(0, 0, 0, 0.08);
+  box-shadow: inset 0 0 0 0.5px var(--v2-border-border-muted);
   cursor: default;
   pointer-events: none;
 }