Feature Request: Please add Command Code as an Agent harness

**Motivation**

Command Code is an AI coding agent that learns and adapts to a developer's
coding preferences. It would be useful as a coding-focused harness for agents
working in Buzz rooms.

At present, Command Code is not available in Buzz's **Agent harness** selector.
Users who want to try it must work out the installation method, executable
command, arguments, authentication, and ACP compatibility themselves. This
creates unnecessary setup friction and makes the resulting configuration
difficult to support.

**Proposed solution**

Add **Command Code** as a supported entry in the existing **Agent harness**
selector used when creating or editing an agent.

The entry should:

- Display Command Code as a selectable harness.
- Provide a setup guide and link to the upstream project.
- Detect whether the required Command Code executable is installed.
- Show a useful status when Command Code is missing or not configured.
- Explain authentication and provider setup.
- Provide actionable errors for installation, authentication, and launch
failures.
- Launch the harness through Buzz's supported `buzz-acp` / ACP integration.
- Allow the harness to be selected for an individual Buzz agent.

Please also confirm whether Command Code already provides an ACP-over-stdio
server. If it does not, please consider coordinating with the Command Code
maintainers on a supported ACP adapter rather than requiring users to maintain
an unofficial wrapper.

**Alternatives considered**

1. **Custom harness**

Users could define Command Code manually through Buzz's Custom harness
option. This is less discoverable and requires users to know the exact
command, arguments, environment variables, authentication process, and
protocol requirements.

2. **Running Command Code separately**

Users could run Command Code in a terminal outside Buzz, but that loses the
benefit of selecting it as an agent harness inside Buzz rooms and makes it
harder to manage alongside other agents.

3. **An unofficial wrapper**

A user-maintained wrapper could translate Command Code into ACP, but that
would be fragile and difficult to support across Command Code and Buzz
releases.

**Additional context**

Upstream project:

- Website: https://commandcode.ai/
- GitHub organisation: https://github.com/CommandCodeAI/
- Repository: https://github.com/CommandCodeAI/command-code

The requested UI location is the existing **Agent harness** selector shown when
editing an agent. This request is for a harness entry in that selector, not for
a change to Buzz's agent hierarchy or dashboard.

A screenshot of the current harness selector is attached to this issue.

I have not found a confirmed public ACP launch command for Command Code, so the
ACP compatibility and adapter requirement should be validated with the
Command Code maintainers before implementation.

Start at the existing Agent harness selector and the supported buzz-acp/ACP integration mentioned in the issue. First validate with Command Code maintainers whether an ACP-over-stdio server exists; done means a selectable, documented harness with executable detection, setup and authentication guidance, actionable failures, and successful launch through ACP.

Written by the indexing model from the issue text.