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/components/save-bar/project-editor-save-bar.component.html

@@ -1,8 +1,16 @@
 <div class="project-editor-save-bar">
+  @if (draftRestored()) {
+    <div class="project-editor-save-bar-notice">
+      <span>{{ 'builder.draftRestored' | translate }}</span>
+      <button type="button" (click)="dismissDraftRestoredNotice()">{{ 'builder.dismiss' | translate }}</button>
+    </div>
+  }
   <div class="project-editor-save-bar-status">
     <span>{{ (status() === 'published' ? 'builder.statusPublished' : 'builder.statusDraft') | translate }}</span>
     @if (dirty()) {
       <span class="project-editor-save-bar-dirty">{{ 'builder.unsavedChanges' | translate }}</span>
+    } @else if (lastSavedAt()) {
+      <span class="project-editor-save-bar-saved-at">{{ 'builder.lastSaved' | translate }}: {{ formatSavedAt(lastSavedAt()!) }}</span>
     }
     @if (issues().length > 0) {
       <ul class="project-editor-save-bar-issues">
@@ -13,6 +21,7 @@
     }
   </div>
   <div class="project-editor-save-bar-actions">
+    <button type="button" class="project-editor-save-bar-reset" (click)="resetDraft()">{{ 'builder.resetDraft' | translate }}</button>
     <button type="button" (click)="save()">{{ 'builder.save' | translate }}</button>
     <button type="button" [disabled]="issues().length > 0" (click)="publish()">{{ 'builder.publish' | translate }}</button>
   </div>

src/app/features/project-editor/components/save-bar/project-editor-save-bar.component.scss

@@ -25,3 +25,27 @@
 .project-editor-save-bar-actions button + button {
   margin-left: 0.5rem;
 }
+
+.project-editor-save-bar-saved-at {
+  color: var(--muted-foreground, #6b7280);
+  margin-left: 0.5rem;
+  font-size: 0.85em;
+}
+
+.project-editor-save-bar-notice {
+  position: absolute;
+  top: -2.5rem;
+  left: 0;
+  right: 0;
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 0.5rem 1rem;
+  background: var(--info-bg, #eff6ff);
+  color: var(--info, #1d4ed8);
+  border-bottom: 1px solid var(--border, #ddd);
+}
+
+.project-editor-save-bar-reset {
+  color: var(--danger, #b91c1c);
+}

src/app/features/project-editor/components/save-bar/project-editor-save-bar.component.ts

@@ -1,5 +1,6 @@
 import { ChangeDetectionStrategy, Component, inject } from '@angular/core';
 import { TranslatePipe } from '../../../../i18n/translate.pipe';
+import { TranslateService } from '../../../../i18n/translate.service';
 import { ProjectEditorFacade } from '../../facade/project-editor.facade';
 
 @Component({
@@ -12,9 +13,12 @@ import { ProjectEditorFacade } from '../../facade/project-editor.facade';
 })
 export class ProjectEditorSaveBarComponent {
   private readonly facade = inject(ProjectEditorFacade);
+  private readonly translate = inject(TranslateService);
   readonly dirty = this.facade.dirty;
   readonly status = this.facade.status;
   readonly issues = this.facade.validationIssues;
+  readonly lastSavedAt = this.facade.lastSavedAt;
+  readonly draftRestored = this.facade.draftRestored;
 
   save(): void {
     this.facade.save();
@@ -23,4 +27,18 @@ export class ProjectEditorSaveBarComponent {
   publish(): void {
     this.facade.publish();
   }
+
+  resetDraft(): void {
+    if (confirm(this.translate.t('builder.confirmResetDraft'))) {
+      this.facade.resetDraft();
+    }
+  }
+
+  formatSavedAt(timestamp: number): string {
+    return new Date(timestamp).toLocaleTimeString();
+  }
+
+  dismissDraftRestoredNotice(): void {
+    this.facade.dismissDraftRestoredNotice();
+  }
 }