[codex] Reclaim abandoned queue reservations

[RoyZhao1991]

Summary

• adds reservation metadata to dequeued scheduler jobs, including worker owner, expiry, and a reservation token
• reclaims worker-disconnect and expired reservations idempotently back to the original queue without changing task ids
• rejects stale completion/failure attempts that present an old reservation token after a task is redelivered
• records audit events for reservations, reclaims, rejections, completions, and retries without including task payload data
• exports AgentStatus and uses a re-entrant metrics lock so the current full suite passes on main

Validation

• uv run pytest tests/test_scheduler.py -q
• uv run pytest -q
• uv run flake8 src/orchestrator/scheduler.py tests/test_scheduler.py src/agent/__init__.py src/common/metrics.py
• uv run python -m py_compile src/orchestrator/scheduler.py tests/test_scheduler.py src/agent/__init__.py src/common/metrics.py
• git diff --check

Fixes #1835