Default Agent Selection

### Describe the feature or problem you'd like to solve

Allow an option to select a default agent so it has all your development context loaded by default without ruining the default agent

### Proposed solution

_No response_

### Example prompts or workflows

_No response_

### Additional context

_No response_

The issue names no files, tests, or entry points. Start by clarifying how a user chooses a default agent and how that setting should coexist with the current default; done means the CLI loads the selected agent's development context by default without changing existing behavior otherwise.

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