fix(plugins): commit the gradlew exec bit for the loader mods

All three vendored wrappers were tracked as 100644, so the README's documented
'plugins/<loader>/gradlew -p plugins/<loader> build' failed on every fresh
clone with 'Permission denied' (exit 126) — and since no install path or CI job
ever ran them, nothing caught it.

git update-index --chmod=+x for the three files; the VM then built all three
modules for the first time (results in the gate commit and the audit).