[Feature]: Agent settings for different steps/usage caps

Problem / Use Case

Problem - if I hit my limit it doesn't automatically switch to a different model or agent. Also if I want to use a different agent for each step its hard to switch over.

Proposed Solution

In settings add preferred agent for different steps, eg Fable for research, Opus for design, GPT luna for implementation, GPT sol for reviews etc

So when I move to each step it will choose the agent I've selected as my preferred agent for that job.

Have the ability to turn on "back up agent"

Then if I've hit my limit or an agent isn't available it then switches to the backup agent I've selected.

Alternative Solutions Considered

Additional Context

Related Issues/PRs:

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