fix(project-editor): editable nav link labels per locale, add LocaleTabs

- navigation-section: add LocaleTabs; label input now reads/writes the
  active locale's translation via a new editableLabel() helper instead of
  always the default locale. facade.updateNavLinkLabel() gained an optional
  locale param (defaults to current default locale, so existing callers
  are unaffected) and correctly promotes a plain-string label into a
  per-locale map when writing a non-default locale.
- languages-section: wrap in SectionCard, add LocaleTabs for consistency.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -4,11 +4,13 @@ import { ProjectEditorFacade } from '../facade/project-editor.facade';
 import { TranslatePipe } from '../../../i18n/translate.pipe';
 import { ButtonComponent } from '../../../shared/ui/button/button.component';
 import { InputComponent } from '../../../shared/ui/input/input.component';
+import { SectionCardComponent } from '../../../shared/ui/section-card/section-card.component';
+import { LocaleTabsComponent } from '../../../shared/ui/locale-tabs/locale-tabs.component';
 
 @Component({
   selector: 'app-project-editor-languages-section',
   standalone: true,
-  imports: [FormsModule, TranslatePipe, ButtonComponent, InputComponent],
+  imports: [FormsModule, TranslatePipe, ButtonComponent, InputComponent, SectionCardComponent, LocaleTabsComponent],
   templateUrl: './languages-section.component.html',
   styleUrls: ['./section.shared.scss'],
   changeDetection: ChangeDetectionStrategy.OnPush
@@ -18,8 +20,15 @@ export class ProjectEditorLanguagesSectionComponent {
   readonly bootstrap = this.facade.bootstrap;
   readonly locales = computed(() => this.bootstrap()?.localization.supportedLocales ?? []);
   readonly defaultLocale = computed(() => this.bootstrap()?.localization.defaultLocale ?? '');
+  readonly supportedLocales = computed(() => this.bootstrap()?.tenant.supportedLocales ?? []);
+  readonly tenantDefaultLocale = computed(() => this.bootstrap()?.tenant.defaultLocale ?? '');
+  readonly activeLocale = signal<string | null>(null);
   readonly newLocale = signal('');
 
+  onActiveLocaleChange(locale: string): void {
+    this.activeLocale.set(locale);
+  }
+
   updateNewLocale(value: string): void {
     this.newLocale.set(value);
   }