Add the BioMixer replacement visualizer

[alexandrutodor]

Summary

• use ontoportal/biomixer-visualizer as the existing optional ontopanel service source and image
• add a Helm overlay and same-host /visualizer ingress route
• pass the replacement URL to Web UI for Helm and Compose deployments
• include the visualizer in the public source-build matrix and deployment documentation

This integrates the new replacement rather than deploying the legacy BioMixer repository. Web UI support is in ontoportal/ontoportal_web_ui#74 and administrator documentation is in ontoportal/documentation#104.

Validation

• make validate
• make validate-generated
• Helm lint and template with values/addons/biomixer-visualizer.yaml
• source-build matrix assertions for the visualizer repository and image
• Compose render assertions for the service, image, and browser URL
• git diff --check

[alexandrutodor]

Deployment note: ghcr.io/ontoportal/biomixer-visualizer:main has been published, but the package is currently private because the OntoPortal organization disables public package visibility. An organization administrator must allow public packages and make this package public before the default image can be pulled without registry credentials. The source-build path remains available in the meantime.