Standardize action and region loading states

Keep progress inside the initiating Button/IconButton or centered within a
LoadingRegion without changing layout or unmounting live content. Document
ownership and completion/error behavior in the registry and living catalog.

Validation: qualified NET02 DG build/typecheck/registry/loading tests;
existing browser geometry, theme and error lifecycle acceptance. All eleven
committed files match the qualified source artifact byte for byte.

packages/ui-react/src/Button.tsx

@@ -1,6 +1,7 @@
 import { forwardRef, type ButtonHTMLAttributes, type ReactNode } from "react";
 import { createAccentVariables, type RgbTuple } from "@nodedc/ui-core";
 import { cn } from "./cn.js";
+import { ActivityIndicator } from "./ActivityIndicator.js";
 
 export type ButtonVariant = "primary" | "secondary" | "ghost" | "danger" | "accent";
 export type ButtonSize = "default" | "compact" | "dense";
@@ -15,6 +16,8 @@ export interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
   shape?: ButtonShape;
   accent?: RgbTuple;
   icon?: ReactNode;
+  /** Pending state belongs to this action; dimensions and accessible name stay unchanged. */
+  loading?: boolean;
 }
 
 export const Button = forwardRef<HTMLButtonElement, ButtonProps>(function Button({
@@ -29,6 +32,8 @@ export const Button = forwardRef<HTMLButtonElement, ButtonProps>(function Button
     children,
     style,
     type = "button",
+    loading = false,
+    disabled,
     ...props
   }, ref) {
     const accentStyle = accent ? createAccentVariables(accent) : undefined;
@@ -44,9 +49,15 @@ export const Button = forwardRef<HTMLButtonElement, ButtonProps>(function Button
         data-shape={shape === "default" ? undefined : shape}
         style={accentStyle ? { ...accentStyle, ...style } : style}
         {...props}
+        disabled={disabled || loading}
+        aria-busy={loading || props["aria-busy"]}
+        data-loading={loading || undefined}
       >
+        <span className="nodedc-button__content">
         {icon ? <span className="nodedc-button__icon" aria-hidden="true">{icon}</span> : null}
         {children}
+        </span>
+        {loading ? <span className="nodedc-action-loading" aria-hidden="true"><ActivityIndicator size="compact" /></span> : null}
       </button>
     );
   });
@@ -54,6 +65,7 @@ export const Button = forwardRef<HTMLButtonElement, ButtonProps>(function Button
 export interface IconButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
   label: string;
   shape?: "circle" | "rounded";
+  loading?: boolean;
 }
 
 export const IconButton = forwardRef<HTMLButtonElement, IconButtonProps>(function IconButton({
@@ -62,6 +74,8 @@ export const IconButton = forwardRef<HTMLButtonElement, IconButtonProps>(functio
   className,
   children,
   type = "button",
+  loading = false,
+  disabled,
   ...props
 }, ref) {
   return (
@@ -73,8 +87,12 @@ export const IconButton = forwardRef<HTMLButtonElement, IconButtonProps>(functio
       aria-label={label}
       title={label}
       {...props}
+      disabled={disabled || loading}
+      aria-busy={loading || props["aria-busy"]}
+      data-loading={loading || undefined}
     >
       {children}
+      {loading ? <span className="nodedc-action-loading" aria-hidden="true"><ActivityIndicator size="compact" /></span> : null}
     </button>
   );
 });