Port task commands to jr task

Integrate the existing Omni/Task functionality into jr. 'jr task ...' should behave exactly like the current 'task ...' command. Reference Plan: /home/ben/omni/_/llm/PLAN_Jr_Evolution.md. Acceptance Criteria: jr task list works, jr task create works, jr task show works, all Omni/Task commands accessible via jr task, reuses Omni.Task logic.