[Bug]: Fix `container system * --prefix` options?

### I have done the following

- [x] I have searched the existing issues
- [x] If possible, I've reproduced the issue using the 'main' branch of this project

### Steps to reproduce

These subcommands apply a prefix but currently this is dead code because `container system start` never configures a prefix. We should allow the launch service label and XPC path to be configurable so that other apps can make use of container library code without conflicting with the container application.

This could also allow homebrew container to run without conflict with a version installed from the release page.

### Current behavior

I run `container system status` or `container system stop` with the `--prefix` option.

It will always fail because the API server will never be set up with the prefix by `container system start`.

### Expected behavior

A test of this capability would be able to I can `start` with an alternate app-root and launch/XPC prefix, and run two separate instances of container services without conflict.

### Environment

```markdown
- OS: 26 beta
- Xcode: Xcode 26 beta
- Container: main
```

### Relevant log output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct