feat(pi-agent-team): separate team and round lifecycle

[geminixiang]

Summary

• Separate the stable retained team handle (teamId) from per-objective round execution (roundId / roundIndex).
• Expose explicit team lifecycle and current/latest RoundRun state while preserving backwards-compatible flat round fields and stable tool handles.
• Retain bounded terminal round summaries and member session identities across continuation rounds.
• Make cancellation terminalize the current round without destroying the retained team, and prevent late completion from contaminating a successor round.
• Include explicit team handle, round identity, objective, and outcome in the foreground manifest.

Evaluation-first

The lifecycle evaluation specification was frozen before implementation. Production code and lifecycle tests were then implemented separately and cross-validated against the frozen acceptance suite, including cancellation races, continuation session stability, bounded history, privacy, wait transitions, and foreground observability.

Before / after

Before: one run identity and status surface conflated the retained team with its latest objective execution; cancellation left continuation semantics ambiguous; rounds had no first-class identity or bounded history.

After: teamId is a stable retained handle, each objective is an explicit RoundRun with a unique roundId and monotonic roundIndex, team lifecycle is distinct from round status/outcome, cancellation returns the team to available, and continuation reuses the same member sessions.

Verification

• npm test --workspace @geminixiang/pi-agent-team: 149/149 passed
• npm run check --workspace @geminixiang/pi-agent-team: TypeScript passed

Scope boundaries

This change intentionally does not include:

• game or scenario domain logic
• cross-process durability or recovery
• typed claim namespaces
• block-reason privacy redesign
• wait-abort wording changes
• semantic or idempotent group aliases