chore(angular): migrate from Angular 18 to 21 via ng update

- Update @angular/* and tooling from 18 → 19 → 20 → 21
- Remove @angular-builders/custom-webpack (unused)
- Apply migrations: standalone implicit default, *ngIf → @if control flow, moduleResolution → bundler

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: AlisherAmonulloev

Angular/angular.json

@@ -111,5 +111,31 @@
   },
   "cli": {
     "analytics": "4497732b-a111-4449-ba60-83332c3ecf94"
+  },
+  "schematics": {
+    "@schematics/angular:component": {
+      "type": "component"
+    },
+    "@schematics/angular:directive": {
+      "type": "directive"
+    },
+    "@schematics/angular:service": {
+      "type": "service"
+    },
+    "@schematics/angular:guard": {
+      "typeSeparator": "."
+    },
+    "@schematics/angular:interceptor": {
+      "typeSeparator": "."
+    },
+    "@schematics/angular:module": {
+      "typeSeparator": "."
+    },
+    "@schematics/angular:pipe": {
+      "typeSeparator": "."
+    },
+    "@schematics/angular:resolver": {
+      "typeSeparator": "."
+    }
   }
 }