fix(project-editor): close redo-staleness window, dedupe footer URL check

Independent review pass over the Configuration Engine sprint (M1-M6).

- Facade: a fresh edit burst now clears the redo (future) stack immediately,
  not just once its debounced commit lands ~300ms later. Previously, editing
  right after an undo left canRedo() true for that window; clicking Redo
  during it would have silently discarded the new edit and jumped back to
  the stale future snapshot. Reordered two interspersed imports/interface
  for readability while in the file.
- footer-section: removed a local HTTP_URL regex + duplicate isValidUrl
  logic (its "shared/ui can't import features" justification didn't apply -
  this file already lives in features/project-editor/sections/, the same
  feature as schema/validators/). Now calls isValidHttpUrl from
  schema/validators/primitives, closing a validator duplication the sprint's
  "no duplicated validators" requirement was meant to catch.

Gate: tsc --noEmit, npm test (33/33), arch:check, build all green.

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

src/app/features/project-editor/sections/footer-section.component.ts

@@ -10,9 +10,7 @@ import { KeyValueEditorComponent } from '../../../shared/ui/key-value-editor/key
 import { MediaPickerComponent } from '../../../shared/media/media-picker/media-picker.component';
 import { MediaAsset } from '../../../core/media/models/media-asset.model';
 import { FooterPaymentIconConfig, FooterSocialLinkConfig } from '../../../shared/models/config';
-
-/** Mirrors the HTTP_URL check in project-validator.service.ts (kept as a local duplicate: shared/ui must not import from features). */
-const HTTP_URL = /^https?:\/\/\S+$/;
+import { isValidHttpUrl } from '../schema/validators/primitives';
 
 type FooterMediaTarget = 'logo' | { type: 'paymentIcon'; index: number };
 
@@ -118,6 +116,6 @@ export class ProjectEditorFooterSectionComponent {
   }
 
   isValidUrl(url: string): boolean {
-    return !url || HTTP_URL.test(url);
+    return !url || isValidHttpUrl(url);
   }
 }