herdr-estate v0.2.0

- An estate row's `prepare` runs an argv command, no shell, in the
  campaign's workdir before the workspace is closed or created; a
  non-zero exit or a spawn failure refuses the launch and leaves a
  running workspace untouched.
- A `paths` entry that doesn't exist on disk is skipped, with a
  warning, instead of being passed on to the agent.

```sh
herdr plugin install andrewdunndev/herdr-estate --ref v0.2.0
```

The release binaries are for shell use; herdr builds the plugin itself on install.