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.
Updated multiple dependencies including Kotlin, Webpack, and Mocha to their latest versions. The project's JDK was upgraded to version 21, and the Kotlin multiplatform plugin version updated to 2.1.0. This ensures better compatibility, improved performance, and access to new features.
