fix: ship teams compatibility + subagent exit fix for pi 0.62

[tmustier]

Summary

• ship the pending 0.5.2 compatibility update for recent Pi releases
• let leader polling timers unref() so nested/non-interactive Pi processes can exit cleanly
• add 0.5.2 release notes covering both fixes

Validation

• npm run check (passes typecheck/lint; repo still has 2 pre-existing lint warnings in activity-tracker.ts)
• direct repro: pi --mode json -p --no-extensions --extension ./extensions/teams/index.ts ... now exits cleanly instead of hanging
• end-to-end repro from the parent session: trivial subagent(agent:"delegate", ...) call now returns and the parent finishes normally

[tmustier]

Findings

• Code looks good.

Verdict

correct — No P0-P2 issues found in the proposed changes.

[tmustier]

Findings

• Code looks good.

Verdict

correct — No P0-P2 issues found after the follow-up fixes.