feat(inbox): approval-item expiry (TTL) for all approval kinds (#622)

[cagdasyurekli]

Summary

Closes #622.

Pending approvals in the inbox previously had no expiry (coworker/inbox.py) — an approval could sit indefinitely, wedging the suspending agent turn permanently on an approval request that might never be answered, or allowing a user to click allow hours later on stale consent context.

This PR implements TTL and expiry handling across all approval kinds (approval, question, directory, plan, tool):

1. Per-Item Expiry TTL: Added optional expires_at and ttl_seconds parameters to InboxItem, InboxStore.add, and all kind-specific add helpers (add_approval, add_question, add_directory, add_plan, add_tool_request, add_notification).
2. Honored at Resolve and Wait Time:
   • In InboxStore.resolve: late resolutions for expired items are rejected (resolve returns False) and the item auto-resolves as "expired" to prevent acting on stale human consent.
   • In InboxStore.wait: pending items with an expiry wait with an asyncio timeout; when the TTL elapses, the item is auto-resolved as "expired" and unblocks the suspending agent turn.
   • In InboxStore.list / InboxStore.pending / InboxStore.get: pending items whose TTL has elapsed are lazily transitioned to "expired".
3. Turn Resumption Notice:
   • Added ApprovalOutcome.EXPIRED to coworker/engine.py.
   • When an approval item expires, inbox_approver returns ApprovalOutcome.EXPIRED.
   • TurnEngine records the event in the audit trail with status="expired" and returns an informative tool-error response ("approval request expired (TTL elapsed)") so the agent turn resumes gracefully rather than hanging forever.
4. Configurable Default TTL:
   • Added inbox_approval_ttl_seconds: Optional[float] = None to Config (coworker/config.py), passed into InboxStore and TurnEngine defaults.
5. Periodic Scheduler Sweeper:
   • SessionManager._scheduler_tick checks for due expired inbox items and durably resumes parked sessions if needed.

Verification

• Added comprehensive tests in tests/test_inbox.py covering expiry calculation, default TTL, late resolution rejection, list/get filtering, wait timeout auto-resolution, and approver outcome.
• Added test_turn_engine_approval_expired_resumes_with_notice in tests/test_engine.py to verify that expired approvals resume turn execution without wedging and emit the proper audit trail and tool error message.
• Passed full test suites (pytest tests/test_inbox.py tests/test_engine.py tests/test_unattended.py).