Nothing ever compiled these modules — no CI job, no install path — which is
why the gradlew exec-bit bug (previous commit) shipped unnoticed. Add
plugins/test-mods.sh: runs each module's vendored wrapper under JDK 17
(they target the Java-17 Minecraft lines; paper/limbo stay on the JDK 21
gate). ci.yml gains a `mods` job (temurin 17 + setup-gradle, wrapper
pinned per module), release.yml gates both plugin gates before shipping.
README: status now records the server-boot verification, the Building
section pins limbo's `-PlimboVersion=<release>` (the `+` default is
unresolvable from the LOOHP repo) and documents both gates.
