[Team] Add a human-readable authorization and task audit trail #57

Planning ID: TODO-L

Proposed issue / PR title: feat(audit): record collaboration authority and task transitions.

Goal: a person can understand who requested, approved, ran, cancelled and accepted work.

Scope: append-only application audit events for membership/Chief changes, important authorization decisions, task transitions and approvals. Include actor, owner, task/request IDs and timestamps; omit secrets and unnecessary private message bodies. Restrict audit access by owner/room/team scope and expose a minimal task activity view.

Out of scope: compliance certification, tamper-proof claims, external SIEM integration or recording every model token.

Dependencies: TODO-G (#52), TODO-I (#54), TODO-J (#55).

Code area: authorization/task event emission, persistence and existing activity/detail UI.

Acceptance and tests: the pilot task’s visible audit explains the full authority chain; unauthorized users cannot read private owner audit detail; secret-shaped test data is not logged; failed and rejected actions are distinguishable from executed actions. Revocation does not erase relevant historical attribution.

Plan update (2026-10-16, team mode via groups): No separate team-mode subsystem is needed; groups with per-Bot grants cover it, and this is step 5 of the ordered plan on #51 (after #56). Audit events start being emitted in step 1 (#149), so history is not lost. Effort: M.

• Gives: task.actors[], approval records (ownerId, reason, by, stale/denied outcomes), room attribution and room.log.
• Gap: no append-only log; tasks, room.log and approval records are pruned at 200; membership, Chief and grant changes are not logged; no activity view.
• Append-only state.audit: ring of about 2k entries (or audit.jsonl in home). Entry: {at, kind, actorId, ownerId, taskId?, requestId?, roomId?, outcome: executed|rejected|failed, ref}; whitelisted fields only, never bodies or secrets.
• Existing seams: emit from transition, hold / decide / release, reach denials, setGrants, syncDesignatedChief and room-membership join/leave.
• Scoped read endpoint: audit, filtered by owner or room membership window (reuse linesVisibleTo logic). Revocation keeps attribution.
• Timeline on the task card: a task card in the room (kind:'task' lines in room.log) with an expandable timeline.
• Test: include a secret-shaped string and assert it is not logged.

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.