v0.1.1

feat: configurable provider_tool + for_harness constructor (#1)

Lets per-harness wrapper binaries (e.g. animus-provider-gemini) reuse the ACP
client while advertising their own provider_tool and pinning a fixed harness
command, so the kernel routes the harness's models to them and the ACP
transport stays an internal detail.

- AcpConfig.provider_tool (default "acp"; ACP_PROVIDER_TOOL env)
- AcpConfig::for_harness(provider_tool, bin, args, default_model)
- AcpSessionBackend::info() reports the configured provider_tool