Migration Angular 20 -> 21 : fin de la migration securite (0 vulnerabilite npm)

- ng update @angular/core@21 @angular/cli@21 (corrige GHSA-jrmj-c5cx-3cw6, XSS SVG)
- Migration automatique des templates vers le control flow natif (@if/@for, 138 fichiers)
- Correction des 5 `track` invalides generes par la migration (trackBy a 1 argument
  -> track $index) + suppression des fonctions trackBy mortes
- TypeScript 5.9, zone.js 0.15 ; npm audit : 0 vulnerabilite

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

web/src/app/campaigns/arc/arc-view/arc-view.component.ts

@@ -1,5 +1,5 @@
 import { Component, OnInit, OnDestroy } from '@angular/core';
-import { CommonModule } from '@angular/common';
+
 import { ActivatedRoute, Router, RouterModule } from '@angular/router';
 import { forkJoin, of } from 'rxjs';
 import { switchMap } from 'rxjs/operators';
@@ -25,7 +25,7 @@ import { ConfirmDialogService } from '../../../shared/confirm-dialog/confirm-dia
  */
 @Component({
     selector: 'app-arc-view',
-    imports: [CommonModule, RouterModule, LucideAngularModule, ImageGalleryComponent],
+    imports: [RouterModule, LucideAngularModule, ImageGalleryComponent],
     templateUrl: './arc-view.component.html',
     styleUrls: ['./arc-view.component.scss']
 })