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/package.json

@@ -15,14 +15,14 @@
   },
   "private": true,
   "dependencies": {
-    "@angular/animations": "^20.3.24",
-    "@angular/common": "^20.3.24",
-    "@angular/compiler": "^20.3.24",
-    "@angular/core": "^20.3.24",
-    "@angular/forms": "^20.3.24",
-    "@angular/platform-browser": "^20.3.24",
-    "@angular/platform-browser-dynamic": "^20.3.24",
-    "@angular/router": "^20.3.24",
+    "@angular/animations": "^21.2.16",
+    "@angular/common": "^21.2.16",
+    "@angular/compiler": "^21.2.16",
+    "@angular/core": "^21.2.16",
+    "@angular/forms": "^21.2.16",
+    "@angular/platform-browser": "^21.2.16",
+    "@angular/platform-browser-dynamic": "^21.2.16",
+    "@angular/router": "^21.2.16",
     "dompurify": "^3.4.1",
     "lucide-angular": "^1.0.0",
     "marked": "^18.0.2",
@@ -31,9 +31,9 @@
     "zone.js": "~0.15.1"
   },
   "devDependencies": {
-    "@angular-devkit/build-angular": "^20.3.27",
-    "@angular/cli": "^20.3.27",
-    "@angular/compiler-cli": "^20.3.24",
+    "@angular-devkit/build-angular": "^21.2.14",
+    "@angular/cli": "^21.2.14",
+    "@angular/compiler-cli": "^21.2.16",
     "@playwright/test": "^1.59.1",
     "typescript": "~5.9.3"
   }