feat(app-showcase): surface Command Center (JSX) in nav (ADR-0080) (#2457)

* feat(app-showcase): surface the Command Center (JSX) page in nav (ADR-0080)

The kind:'jsx' example page existed + was browser-verified but wasn't reachable
in the showcase app. Add a Pages nav item so it's clickable.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore: retrigger CI (prior run hit transient infra failures)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Jack Zhuang <277994282+os-zhuang@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: os-zhuang

examples/app-showcase/src/apps/index.ts

@@ -65,6 +65,7 @@ export const ShowcaseApp = App.create({
       icon: 'layout',
       children: [
         { id: 'nav_gallery', type: 'page', pageName: 'showcase_component_gallery', label: 'Component Gallery', icon: 'layout-template' },
+        { id: 'nav_command_center_jsx', type: 'page', pageName: 'showcase_command_center_jsx', label: 'Command Center (JSX)', icon: 'code' },
         { id: 'nav_styling_gallery', type: 'page', pageName: 'showcase_styling_gallery', label: 'Styling (ADR-0065)', icon: 'palette' },
         { id: 'nav_page_variables', type: 'page', pageName: 'showcase_page_variables', label: 'Page Variables', icon: 'mouse-pointer-click' },
         { id: 'nav_contact_form', type: 'page', pageName: 'showcase_contact_form', label: 'Contact Form', icon: 'mail-plus' },