cgroup-v2 AllowedCPUs= drop-ins for system/user/build/game slices.
Defaults: core 0 for everything-not-game, cores 1..N-1 for game,
computed from nproc. LEFT4ME_SYSTEM_CPUS / LEFT4ME_GAME_CPUS
overrides; single-core hosts skip with a warning.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
