Using custom agent in background agent doesn't respect model property

[ntrogh]

Testing #280191

• Specify model metadata in custom agent
• Create a new background agent
• Select custom agent

-> The model dropdown for the background agent still shows all models and doesn't switch to the model specified in the custom agent.

I'd expect the background agent to respect and use the model specified in the custom agent.

[DonJayamanne]

Requires api changes, one of the issues that were aware of

[DonJayamanne]

this has been fxied

[eleanorjboyd]

when I switch to my custom agent "debugging" it does not switch to the model I had included in the config still
https://github.com/user-attachments/assets/bf5d79f0-f1d6-4e4e-b689-1facf34b4b45