refactor(builder): extract useNodeProp hook, dedup StylePanel setProp boilerplate

Adopted in BackgroundSectionStylePanel, ButtonStylePanel, ContainerStylePanel,
FormStylePanel, GenericPropsEditor, HeroStylePanel, ImageStylePanel,
MediaStylePanel, NavStylePanel, SectionTypePanel, SocialStylePanel,
TextStylePanel — only where the inline setProp/setPropStyle were behaviorally
identical to the hook. PricingStylePanel and FeaturesEditor keep their own
array-mutation logic since it differs. Behavior-preserving (task E4.1).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/panels/right/styles/ButtonStylePanel.tsx

@@ -12,6 +12,7 @@ import {
   PresetButtonGrid,
   TextInputField,
   autoTextColor,
+  useNodeProp,
 } from './shared';
 
 /* ---------- BUTTON ---------- */
@@ -19,14 +20,7 @@ export const ButtonStylePanel: React.FC<StylePanelProps> = ({ selectedId, nodePr
   const { actions } = useEditor();
   const style: CSSProperties = nodeProps.style || {};
 
-  const setPropStyle = useCallback(
-    (property: string, value: string) => {
-      actions.setProp(selectedId, (props: any) => {
-        props.style = { ...props.style, [property]: value };
-      });
-    },
-    [actions, selectedId],
-  );
+  const { setPropStyle } = useNodeProp(selectedId);
 
   const setButtonColor = useCallback(
     (bgColor: string) => {