[Team] Persist a minimal collaboration task lifecycle #54

Planning ID: TODO-I

Proposed issue / PR title: feat(tasks): track Chief handoffs and requester acceptance.

Goal: make responsibilities and completion visible beyond chat text.

Scope: stable task IDs, origin message/room, requester and responsible Chief/owner, acceptance criteria, allowed state transitions, clarification, cancellation, result artifacts and requester acceptance. A bot result becomes result ready; only an authorized acceptance decision marks it accepted. Link private specialist work to the owner’s task without exposing private transcripts.

Out of scope: task DAGs, project boards and autonomous acceptance based only on model confidence.

Dependencies: TODO-G (#52), TODO-H (#53).

Code area: persistent store and a small task API/model; exchange/group-result integration; task cards in existing chat UI.

Acceptance and tests: one request is accepted, worked, blocked on approval, resumed, returned and accepted by the requester; invalid transitions and wrong-owner cancellation fail. Failed or cancelled execution cannot be displayed as accepted. Every status links to the responsible actor and originating conversation.

Delivery

One focused implementation PR for this issue. This is planned work, not a claim of shipped multi-human support. Preserve the pristine upstream pin and generated patch/client boundaries. Keep team mode disabled until the documented authorization gates pass. Record exact tested head, executed checks, missing checks and independent review. No production credentials or live deployment are part of this issue.