feat(sop): support service-level SOP in agent service

**Background**

Building on top of the SDK-level SOP implementation, the service-level implementation introduces **persistent storage, lifecycle management, and API exposure** for SOPs within agent service.

**Changes**

- **Storage**: support SOP in current storage implementations
- **Service**: add SOP service layer in the service
- **Router**: add SOP related CRUD routers
- **WebUI**: display SOP tasks in the frontend
- Documentation

No files or tests are specified, so start by inspecting the existing SDK-level SOP implementation and any related service/route patterns in this repo. Then locate current storage backends, service-layer modules, CRUD router definitions, and their tests to mirror how another persistent entity is handled in the agent service. Next, identify the WebUI task-list components/pages that should render SOP tasks and map the new API behavior there. Completion is achieved when SOP CRUD is persisted in service storage, exposed via API, reflected in the UI, and docs are updated accordingly.

索引モデルが issue の本文から書いたものです。