Bump elliptic and @angular-devkit/build-angular in /admin-ui

Removes [elliptic](https://github.com/indutny/elliptic). It's no longer used after updating ancestor dependency [@angular-devkit/build-angular](https://github.com/angular/angular-cli). These dependencies need to be updated together.


Removes `elliptic`

Updates `@angular-devkit/build-angular` from 0.803.29 to 21.0.5
- [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/commits/v21.0.5)

---
updated-dependencies:
- dependency-name: elliptic
  dependency-version: 
  dependency-type: indirect
- dependency-name: "@angular-devkit/build-angular"
  dependency-version: 21.0.5
  dependency-type: direct:development
...

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Author: dependabot[bot]