Make model selection feature flags for .com and SM default enabled and GA ready

Summary

This issue is to cleanup the duo_agent_platform_model_selection and ai_user_model_switching feature flag, after the feature flags have been enabled by default for an appropriate amount of time in production.

• duo_agent_platform_model_selection gates DAP namespace model selection for .com
• ai_user_model_switching gates end-user model selection in .com

Both have been enabled globally via chatops on 18/09/2025. See roll out issue for more details.

Owners

• Team: Custom Models
• Most appropriate slack channel to reach out to: #g_custom_models
• Best individual to reach out to: @julie_huang / @manojmj
• PM: @susie.bee

Stakeholders

Expectations

What might happen if this goes wrong?

Cleaning up the feature flag

• Specify in the issue description if this feature will be removed completely or will be productized as part of the Feature Flag cleanup
• Create a merge request to remove <feature-flag-name> feature flag. Ask for review and merge it.
  • Remove all references to the feature flag from the codebase.
  • Remove the YAML definitions for the feature from the repository.
  • Create a changelog entry.
• Ensure that the cleanup MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post.
  • /chatops run auto_deploy status <merge-commit-of-cleanup-mr>
• Close the feature issue to indicate the feature will be released in the current milestone.
• If not already done, clean up the feature flag from all environments by running these chatops command in #production channel: /chatops run feature delete <feature-flag-name> --dev --pre --staging --staging-ref --production
• Close this rollout issue.