Wrong requests after switching app in evaluator playground

[mmabrouk]

Switching from a chat application in the LLM-as-a-judge playground to a completion application keeps sending context and messages from the previous app.

To reproduce:

1. Open a chat application in the LLM-as-a-judge playground.
2. Run it.
3. Switch to a completion application and run again.

The completion request should not send context or messages from the old app.

[linear-code]

AGE-3793