fix(daemon): stop cleanly on Windows

[y4ho0]

Linked issue

Closes #843

What & why

crg-daemon stop polled process state with os.kill(pid, 0) and escalated with signal.SIGKILL. Both assumptions are POSIX-specific: on Windows the liveness probe does not reliably report an exited process, and SIGKILL is unavailable.

The resulting AttributeError also skipped PID cleanup and prevented crg-daemon restart from starting the daemon again.

This change:

• reuses the existing cross-platform pid_alive() helper while waiting for shutdown
• uses SIGKILL when available and falls back to SIGTERM on platforms without it
• clears the daemon PID in a finally block so a failed forced stop cannot leave stale state
• adds mocked Windows regressions for forced stop, restart after exit, and PID cleanup after an escalation failure

How it was tested

uv run --python 3.13 pytest tests/ --tb=short -q
# 2401 passed, 5 skipped, 2 xpassed

uv run pytest tests/test_daemon.py --tb=short -q
# 69 passed

uv run ruff check code_review_graph/ tests/test_daemon.py
# All checks passed

uv run mypy code_review_graph/ --ignore-missing-imports --no-strict-optional
# Success: no issues found in 70 source files

bandit -r code_review_graph/ -c pyproject.toml
# No issues identified

AI assistance

OpenAI Codex was used for repository inspection, implementation and test drafting, local verification, and review of the resulting diff.

Checklist

• Tests added for the corrected behavior
• All tests pass
• Linting passes
• Type checking passes
• Lines are at most 100 characters
• Documentation is not required because the CLI interface and expected behavior are unchanged