Explicit local/test workspace adapter.

This crate provides a concrete implementation of the [Workspace] trait for local filesystem access. It is the counterpart of agent-workspace-server for single-process deployments and testing.

Design decisions

Local-first, portable

The local workspace uses only tokio::fs and tokio::process::Command, requiring no external dependencies beyond the host filesystem. Remote providers (Daytona, Moulin, E2B) are in the agents-runtime crate and may be migrated here in a follow-up.

Path safety

All paths are resolved relative to the workspace root. Absolute paths are accepted but must be within the root or the operation fails.