chore: add new logo (#557)

Add a new logo for the package.

The logo was AI-generated and combines the Angular shield shape with the
single-spa lightning bolt, using Angular's gradient color palette.

Angular's press kit (https://angular.dev/press-kit) explicitly allows
adapting the shield shape and colors for community projects. The logo is
sufficiently distinct from the official Angular logo to avoid confusion.

Author: arturovt