feat: workspace sync + workspace-root

[christso]

Adds config-driven workspace sync (local + git sources, copy/symlink) via agentv workspace create|sync, and adds agentv eval --workspace-root to default provider working directory (cwd/workspaceTemplate) when not set in targets.yaml.

Docs updated and unit tests added for workspace-root behavior.

Changeset: minor bump for agentv.

TODO:

• define workspace in yaml which works for all agent providers.
• clone remote repo if configured - otherwise fallback to existing folder.

[christso]

Superseded by #180 which adds workspace_template config option for isolated eval workspaces. The simpler approach handles the core use case (copy directory to temp location per eval). Future enhancements like git clone can be added via workspace_setup scripts (#177).