Function register_task 

pub fn register_task(
    registry: &Arc<ToolRegistry>,
    llm_client: Arc<dyn LlmClient>,
    agent_registry: Arc<AgentRegistry>,
    workspace: String,
)

Register the task delegation tools (task, parallel_task).

Must be called after the registry is wrapped in Arc. Requires an LLM client and the workspace path so child agent loops can be spawned inline.