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/app.component.html

@@ -3,7 +3,7 @@
 <div class="app-container">
   <app-sidebar></app-sidebar>
 
-  <ng-container *ngIf="sidebarConfig$ | async as config">
+  @if (sidebarConfig$ | async; as config) {
     <app-secondary-sidebar
       [title]="config.title"
       [titleRoute]="config.titleRoute || null"
@@ -11,7 +11,7 @@
       [createActions]="config.createActions"
       [bottomPanel]="config.bottomPanel || null">
     </app-secondary-sidebar>
-  </ng-container>
+  }
 
   <main class="main-content">
     <router-outlet></router-outlet>