Improve ops orchestrator shutdown responsiveness, diagnostics, and tests

[noog6]

Motivation

• Make orchestrator shutdown more responsive under blocked probes or lock contention by waking the loop immediately after requesting stop.
• Reduce contention during probe/tick so shutdown metadata capture can proceed without being blocked by long-critical sections.
• Improve observability of shutdown progress so callers can tell if the loop thread is still alive and emit one final heartbeat when the loop observes the stop request.
• Add tests to cover retry-after-wake join behavior and final-heartbeat emission.

Description

• Added a lightweight loop wake event _loop_wake_event and a shutdown_requested_at marker to OpsOrchestrator and updated start_loop/stop_loop to set the marker, set stop_event, and explicitly wake the loop before joining.
• Implemented a retry join: after the first bounded join times out the code will explicitly wake the loop and yield (time.sleep(0)) then attempt a grace join.
• Reduced lock hold time in _tick by constructing the HealthSnapshot while holding the lock but emitting the snapshot after releasing the lock to avoid long critical sections.
• Added _wake_loop and _emit_shutdown_heartbeat helpers so the loop emits one final heartbeat/log when it observes stop_event.
• Enhanced main.py shutdown handling to include whether the loop thread is still alive (is_loop_alive()) in the shutdown warning and to emit explicit follow-up guidance when stop_loop returns timed_out.
• Extended and updated unit tests in tests/ covering timeout/warning behavior, lock contention handling, explicit wake + retry behavior, and final heartbeat emission, and adjusted tests/test_main_ops_shutdown_warning.py to assert the new logging behavior.

Testing

• Performed environment setup command: python -m pip install pyyaml -q which completed successfully.
• Ran targeted unit tests: pytest -q tests/test_ops_orchestrator_shutdown.py tests/test_main_ops_shutdown_warning.py and observed 12 passed in 0.59s.
• All modified and related shutdown tests passed locally.

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Codex Task