[Feature]: support using OpenCode agents in custom hats

[francocalvo]

Use case

When using a multi hat ralph loop, it would be excellent to be able to pass the --agent flag to Opencode.
For example, I already have the 'planner' and 'builder' agents for me, with it's own permissions, default model and so on.

Proposed solution

Add the 'agent' property to the custom hat configuration.

Area

CLI

Backend(s) impacted

No response

Alternatives considered

No response

Additional context

No response

[mikeyobrien]

You should be already able do this by passing args: ["--agent", "name"]

[francocalvo]

Incredible. Thank you! This really ticks most of the things I imagined for a tool like this! :D