feat(ui): add activity indicator governance

packages/ui-core/styles.css

@@ -211,6 +211,30 @@
   transform: scale(var(--nodedc-icon-glyph-scale));
 }
 
+.nodedc-activity-indicator {
+  display: inline-block;
+  width: 1.125rem;
+  height: 1.125rem;
+  flex: 0 0 auto;
+  box-sizing: border-box;
+  border: 2px solid currentColor;
+  border-inline-end-color: transparent;
+  border-radius: var(--nodedc-radius-circle);
+  color: inherit;
+  opacity: 0.78;
+  animation: nodedc-activity-indicator-spin 780ms linear infinite;
+}
+
+.nodedc-activity-indicator[data-size="compact"] {
+  width: 0.875rem;
+  height: 0.875rem;
+  border-width: 1.5px;
+}
+
+@keyframes nodedc-activity-indicator-spin {
+  to { transform: rotate(360deg); }
+}
+
 .nodedc-icon-button {
   display: inline-grid;
   width: var(--nodedc-icon-button-size);
@@ -3585,6 +3609,7 @@ textarea.nodedc-field__control {
 }
 
 @media (prefers-reduced-motion: reduce) {
+  .nodedc-activity-indicator,
   .nodedc-dropdown-surface,
   .nodedc-overlay,
   .nodedc-window,