Migration des builders Angular vers @angular/build

Remplace @angular-devkit/build-angular (déprécié, chaîne Webpack) par
@angular/build sur les 4 cibles (build, serve, extract-i18n, test), ce
qui supprime l'avertissement de dépréciation du dev-server. Le paquet
@angular-devkit/build-angular est retiré des devDependencies au profit
de @angular/build ; lockfile resynchronisé.

Builds production et development vérifiés. (Karma reste exécutable ;
aucune config Karma custom ajoutée.)

frontend/angular.json

@@ -19,7 +19,7 @@
       "prefix": "app",
       "architect": {
         "build": {
-          "builder": "@angular-devkit/build-angular:application",
+          "builder": "@angular/build:application",
           "options": {
             "outputPath": "dist/schotziad-km-tracker",
             "index": "src/index.html",
@@ -68,7 +68,7 @@
           "defaultConfiguration": "production"
         },
         "serve": {
-          "builder": "@angular-devkit/build-angular:dev-server",
+          "builder": "@angular/build:dev-server",
           "configurations": {
             "production": {
               "buildTarget": "schotziad-km-tracker:build:production"
@@ -80,13 +80,13 @@
           "defaultConfiguration": "development"
         },
         "extract-i18n": {
-          "builder": "@angular-devkit/build-angular:extract-i18n",
+          "builder": "@angular/build:extract-i18n",
           "options": {
             "buildTarget": "schotziad-km-tracker:build"
           }
         },
         "test": {
-          "builder": "@angular-devkit/build-angular:karma",
+          "builder": "@angular/build:karma",
           "options": {
             "polyfills": [
               "zone.js",