arch(sprint1): add unknown widget fallback diagnostics

src/app/widgets/ui/index.ts

@@ -1,3 +1,4 @@
 export * from './footer-navigation-widget.component';
 export * from './hero-widget.component';
 export * from './product-carousel-widget.component';
+export * from './unknown-widget.component';

src/app/widgets/ui/unknown-widget.component.ts

@@ -0,0 +1,38 @@
+import { ChangeDetectionStrategy, Component, Input } from '@angular/core';
+
+@Component({
+  selector: 'app-unknown-widget',
+  standalone: true,
+  template: `
+    <section class="unknown-widget" role="status" aria-live="polite">
+      <strong>Widget unavailable</strong>
+      <p>{{ widgetType }}@{{ widgetVersion }}</p>
+    </section>
+  `,
+  styles: [
+    `
+      .unknown-widget {
+        border: 1px dashed var(--border-color, #d3dad9);
+        border-radius: var(--radius-md, 12px);
+        padding: 0.75rem;
+        color: var(--text-secondary, #667a77);
+        background: var(--background-secondary, #f5f5f5);
+      }
+
+      .unknown-widget strong {
+        display: block;
+        font-size: 0.9rem;
+      }
+
+      .unknown-widget p {
+        margin: 0.25rem 0 0;
+        font-size: 0.8rem;
+      }
+    `
+  ],
+  changeDetection: ChangeDetectionStrategy.OnPush
+})
+export class UnknownWidgetComponent {
+  @Input() widgetType: string = 'unknown';
+  @Input() widgetVersion: string = 'unknown';
+}