Added a Gradle build script for the test-app module with Kotlin Multiplatform configuration, including JS and JVM targets. Upgraded Kotlin plugin version to 2.1.10, updated dependencies, and adjusted the JS distribution path. Renamed the JS file in UndertowServer configuration for accuracy.
Introduced a new `test-app` module with a basic Kotlin/JS UI and a Kotlin/JVM backend. Updated dependencies to use `api` where applicable and made configuration changes to support composite builds.
