Display deep research costs for admin users after OpenAI service returns cost headers

## Summary When an admin user performs a deep research search, the costs should be displayed. Before this can be implemented, the internal OpenAI service must respond with cost information in its headers, similar to how the research service currently does. ## Steps to Reproduce Not provided. ## Expected Behaviour Admin users should see the costs associated with a deep research search. ## Actual Behaviour Costs are not displayed for deep research searches. ## Environment Not provided. --- *Reported by **retoor** via DevPlace.*