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/playthrough/playthrough-flags-page/playthrough-flags-page.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 } from 'rxjs';
 import { LucideAngularModule, ArrowLeft } from 'lucide-angular';
@@ -20,7 +20,7 @@ import { PlaythroughFlagsManagerComponent } from '../../../shared/playthrough-fl
  */
 @Component({
     selector: 'app-playthrough-flags-page',
-    imports: [CommonModule, RouterModule, LucideAngularModule, PlaythroughFlagsManagerComponent],
+    imports: [RouterModule, LucideAngularModule, PlaythroughFlagsManagerComponent],
     templateUrl: './playthrough-flags-page.component.html',
     styleUrls: ['./playthrough-flags-page.component.scss']
 })