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/shared/rooms-editor/rooms-editor.component.ts

@@ -1,5 +1,5 @@
 import { Component, EventEmitter, Input, Output } from '@angular/core';
-import { CommonModule } from '@angular/common';
+
 import { FormsModule } from '@angular/forms';
 import { LucideAngularModule, Plus, Trash2, ChevronDown, ChevronUp, GitBranch, X } from 'lucide-angular';
 import { Room, RoomBranch } from '../../services/campaign.model';
@@ -15,7 +15,7 @@ import { Room, RoomBranch } from '../../services/campaign.model';
  */
 @Component({
     selector: 'app-rooms-editor',
-    imports: [CommonModule, FormsModule, LucideAngularModule],
+    imports: [FormsModule, LucideAngularModule],
     templateUrl: './rooms-editor.component.html',
     styleUrls: ['./rooms-editor.component.scss']
 })