Remove the separate langbot_box_runtime Docker service. Box Runtime
now always launches as a local stdio subprocess, regardless of whether
LangBot runs in Docker or not. The WebSocket transport path is kept
only for explicit runtime_url configuration (remote deployment).
This simplifies deployment by eliminating cross-container path mapping
and network hops. Box Runtime is a pure scheduling process (talks to
Docker socket / nsjail), it does not execute user code or touch the
filesystem, so container isolation is unnecessary — unlike Plugin
Runtime.
Extract self-contained box runtime modules (actions, backend, client,
errors, models, runtime, security, server) to langbot-plugin-sdk and
update all imports to use `langbot_plugin.box.*`. Keep only service
and
connector in LangBot core as they depend on the Application context.
- Update docker-compose to use `langbot_plugin.box.server` entry
point
- Update pyproject.toml to use local SDK via `tool.uv.sources`
- Remove migrated source files and their unit/integration tests
- Update remaining test imports to match new module paths
