feat(sprint18): editor autosave/reset, admin auth, QR reuse, Ed25519 prep

- Project editor: persist draft to localStorage, restore on reload,
  last-saved/draft-restored status indicators, section/whole-draft reset
  with confirmation.
- Extract shared QR/polling/expiry engine from TelegramLoginComponent
  (shared/qr-login) and reuse it for a new admin login flow.
- Admin authentication kept fully separate from customer session:
  own cookie/localStorage keys, signals, guard, and header interceptor
  (core/admin-auth).
- ?login=true / ?adminLogin=true open the respective login dialog for
  manual testing.
- Ed25519 challenge/verify interfaces (fail-closed no-op binding) ready
  for backend delivery.
- Document autosave/reset/admin-auth/QR-reuse/Ed25519 model and the
  remaining full-field-coverage gap in docs/Project-Editor.md.

src/app/features/project-editor/pages/project-editor-page.component.html

@@ -13,6 +13,11 @@
     </section>
   } @else {
     <section class="project-editor-stack">
+      @if (canResetActiveSection()) {
+        <div class="project-editor-section-actions">
+          <button type="button" (click)="resetActiveSection()">{{ 'builder.resetSection' | translate }}</button>
+        </div>
+      }
       @switch (activeSection()) {
         @case ('general') { <app-project-editor-general-section /> }
         @case ('branding') { <app-project-editor-branding-section /> }

src/app/features/project-editor/pages/project-editor-page.component.scss

@@ -25,6 +25,20 @@
   gap: 16px;
 }
 
+.project-editor-section-actions {
+  display: flex;
+  justify-content: flex-end;
+}
+
+.project-editor-section-actions button {
+  color: #b91c1c;
+  background: transparent;
+  border: 1px solid #d3dad9;
+  border-radius: 8px;
+  padding: 6px 12px;
+  cursor: pointer;
+}
+
 .project-editor-empty {
   min-height: 240px;
   display: grid;

src/app/features/project-editor/pages/project-editor-page.component.ts

@@ -16,9 +16,10 @@ import { ProjectEditorLanguagesSectionComponent } from '../sections/languages-se
 import { ProjectEditorNavigationSectionComponent } from '../sections/navigation-section.component';
 import { ProjectEditorPreviewSectionComponent } from '../sections/preview-section.component';
 import { TranslatePipe } from '../../../i18n/translate.pipe';
+import { TranslateService } from '../../../i18n/translate.service';
 import { StaticPagesEditorComponent } from '../../content-management/components/static-pages-editor.component';
 import { ProjectEditorSaveBarComponent } from '../components/save-bar/project-editor-save-bar.component';
-import { ProjectEditorSectionId } from '../models/project-editor.model';
+import { EDITOR_SECTION_BOOTSTRAP_KEYS, ProjectEditorSectionId } from '../models/project-editor.model';
 
 const KNOWN_SECTIONS: ProjectEditorSectionId[] = [
   'general', 'branding', 'theme', 'header', 'footer', 'homepage', 'widgets', 'static-pages', 'features', 'languages', 'navigation', 'preview'
@@ -51,8 +52,10 @@ const KNOWN_SECTIONS: ProjectEditorSectionId[] = [
 export class ProjectEditorPageComponent {
   readonly facade = inject(ProjectEditorFacade);
   private readonly route = inject(ActivatedRoute);
+  private readonly translate = inject(TranslateService);
   readonly bootstrap = this.facade.bootstrap;
   readonly activeSection = this.facade.activeSection;
+  readonly canResetActiveSection = () => !!EDITOR_SECTION_BOOTSTRAP_KEYS[this.activeSection()];
 
   private readonly routeSection = toSignal(
     this.route.paramMap.pipe(map(params => params.get('section') as ProjectEditorSectionId | null)),
@@ -69,6 +72,12 @@ export class ProjectEditorPageComponent {
     });
   }
 
+  resetActiveSection(): void {
+    if (confirm(this.translate.t('builder.confirmResetSection'))) {
+      this.facade.resetSection(this.activeSection());
+    }
+  }
+
   @HostListener('window:beforeunload', ['$event'])
   warnBeforeUnload(event: BeforeUnloadEvent): void {
     if (this.facade.dirty()) {