Fix install.sh version detection when no latest release exists

When no releases are tagged as latest, the GitHub redirect URL lacks a
/tag/ segment, so the sed substitution is a no-op and $VERSION gets set
to the full URL rather than being empty. Validate that $VERSION matches
a semver pattern instead of just checking for empty.

Fixes #36

Co-Authored-By: Cassondra <1840295+castastrophe@users.noreply.github.com>

Author: monorkin

scripts/install.sh

@@ -23,7 +23,7 @@ esac
 # Fetch latest version
 echo "Fetching latest version..."
 VERSION=$(curl -sI "https://github.com/$REPO/releases/latest" | grep -i '^location:' | sed 's/.*tag\///' | tr -d '\r\n')
-if [ -z "$VERSION" ]; then
+if ! [[ "$VERSION" =~ ^v?[0-9]+\.[0-9]+\.[0-9]+ ]]; then
   echo "Failed to determine latest version"
   exit 1
 fi