Add golden snapshot trigger workflow

[pabloelisseo]

Summary

• add a short-lived manual workflow that submits one golden snapshot request for an exact main commit
• validate required repository secrets, SHA input, and backend acceptance response
• keep final snapshot status in the commit-specific Golden Snapshot check and Slack instead of occupying a runner

Validation

• workflow YAML parsed successfully
• embedded request flow and response validation checked
• minimal contents: read permission; no checkout or package installation

Dependency

Enable after https://github.com/BuilderIO/ai-services/pull/6173 is deployed and these repository secrets are configured:

• BUILDER_PROJECT_API_KEY
• BUILDER_SUPERUSER_TOKEN (dedicated non-personal service/superuser token)