test(daemon): stop probing real PIDs in test_is_daemon_running_dead

The test patched os.kill, but on Windows pid_alive uses OpenProcess, so
the mock was bypassed and the test asserted against the runner's real
PID space; PID 9999 exists occasionally (PID reuse) and the CI job
flaked. Patch pid_alive at the module seam instead, which also keeps
the stale-PID-file cleanup covered on Windows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FmPUotoqsNWWt3b41FMjwv