* Mark the two doc-invoked host scripts executable
README, AGENTS, CONTRIBUTING and docs/seam.md run scripts/build-host.sh
directly, and docs/benchmarks.md runs scripts/bench-run.sh the same way,
but both are committed 100644, so a fresh POSIX clone answers permission
denied at the first documented step. Windows trees never see the mode
bit, which is likely how it went unnoticed.
* Mark the remaining host scripts executable too
Per the discussion in #163: leaving only the two doc-invoked scripts
executable hides the next instance of the same failure behind an
inconsistent set, so all five scripts/*.sh get the bit.