feat(builder): implement professional content management experience

Content dashboard with real published/draft/SEO-health/completion metrics and a recommended-next-action; static pages editor rebuilt as visual page cards (icon/status/SEO badge/last edited) with legal pages surfaced first; full-page editor grouped into Content/SEO/Sharing/Advanced tabs, raw HTML moved behind an Advanced disclosure; hero image now supports alt text and caption; content-health-widget is a reusable checklist+completion component.

src/app/shared/models/config/static-page.model.ts

@@ -60,8 +60,12 @@ export interface StaticPageConfig {
   status?: 'draft' | 'published';
   customTemplate?: string;
   heroImage?: string;
+  heroImageAlt?: string;
+  heroImageCaption?: string;
   thumbnail?: string;
   gallery?: string[];
+  /** ISO timestamp set whenever the page is saved; drives the CMS content dashboard's last-edited/health metrics. */
+  updatedAt?: string;
 }
 
 export interface LegacyStaticPageConfig {