Bump rollup and @angular-devkit/build-angular in /samples/spa-client

Bumps [rollup](https://github.com/rollup/rollup) to 4.59.0 and updates ancestor dependency [@angular-devkit/build-angular](https://github.com/angular/angular-cli). These dependencies need to be updated together.


Updates `rollup` from 4.22.4 to 4.59.0
- [Release notes](https://github.com/rollup/rollup/releases)
- [Changelog](https://github.com/rollup/rollup/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rollup/rollup/compare/v4.22.4...v4.59.0)

Updates `@angular-devkit/build-angular` from 18.2.11 to 21.2.0
- [Release notes](https://github.com/angular/angular-cli/releases)
- [Changelog](https://github.com/angular/angular-cli/blob/main/CHANGELOG.md)
- [Commits](https://github.com/angular/angular-cli/compare/18.2.11...v21.2.0)

---
updated-dependencies:
- dependency-name: rollup
  dependency-version: 4.59.0
  dependency-type: indirect
- dependency-name: "@angular-devkit/build-angular"
  dependency-version: 21.2.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

samples/spa-client/package.json

@@ -23,7 +23,7 @@
     "zone.js": "~0.14.10"
   },
   "devDependencies": {
-    "@angular-devkit/build-angular": "^18.2.11",
+    "@angular-devkit/build-angular": "^21.2.0",
     "@angular/cli": "^18.2.11",
     "@angular/compiler-cli": "^18.2.0",
     "@types/jasmine": "~5.1.0",