Fix project root build/libs dir not being cleaned

The base plugin is usually applied by the java plugin, but since that has been moved into the platforms, cleaning was no longer applied to the root dir (created and filled by the universal submodule).

build.gradle.kts

@@ -1,6 +1,7 @@
 import org.gradle.api.plugins.JavaPlugin.TEST_IMPLEMENTATION_CONFIGURATION_NAME
 
 plugins {
+    base
     id("via.build-logic")
 }