[BUG]: GRAALVM_HOME is not set for GraalVM early-access builds such as 26-ea+13-graal #89

Version
vfox-java main (bfcdbcc), vfox 1.0.13

OS
Linux

Describe the bug
Since #57, vfox install java@26.ea.13-graal installs Oracle GraalVM's early-access builds, named 26-ea+13-graal. Using one sets JAVA_HOME but not GRAALVM_HOME, which GraalVM's GA builds get (the e2e suite checks it for 25.0.2-graalce):

$ vfox install java@26.ea.13-graal
...
Install java@26-ea+13-graal success!
$ vfox use --global java@26-ea+13-graal
Now using java@26-ea+13-graal.
$ java -version
java version "26" 2026-03-17
Java(TM) SE Runtime Environment Oracle GraalVM 26-dev+13.1 (build 26+13-jvmci-b01)
Java HotSpot(TM) 64-Bit Server VM Oracle GraalVM 26-dev+13.1 (build 26+13-jvmci-b01, mixed mode, sharing)
$ echo "JAVA_HOME=$JAVA_HOME"; echo "GRAALVM_HOME=${GRAALVM_HOME-<unset>}"
JAVA_HOME=~/.vfox/sdks/java
GRAALVM_HOME=<unset>

EnvKeys reads the distribution as the second - part of the installed name, which for an early-access build is the build (ea+13):

PreInstall appends -<short name>, then -fx, to Foojay's version, so reading the last part after dropping a trailing -fx would cover these:

Unlike #27, where GRAALVM_HOME stays set after switching away from GraalVM, here it is never set.

Found while working on #86.