SteamInstaller defaults to steamcmd="steamcmd" (bare name), which relies
on PATH lookup. Deployments that don't have steamcmd on PATH — or where
steamcmd.sh's `cd "$(dirname "$0")"` breaks under PATH-symlink invocation
(observed with the Valve-shipped script) — can now pin an absolute path
via LEFT4ME_STEAMCMD. Default keeps bare-name lookup for dev/tests.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>