fix(setup): extract .tar.zst via cwd, not -C (GNU tar stdin quirk)

CI on ubuntu (GNU tar) failed extracting zst snapshots: `tar -xf - -C
<dir>` with a stdin archive mis-parses <dir> as a member operand ("Cannot
open: No such file or directory"), while the gzip path's `-xzf <file> -C
<dir>` is fine. Run tar with cwd=<dataDir> and drop -C — unambiguous on
both GNU tar and bsdtar, and a decode failure now surfaces as a clear EOF
error instead.