chore: refactor Gradle config, standardize Kotlin MPP plugin usage, and update dependencies

- Unified plugin application across modules using `alias(libs.plugins.*)` instead of hardcoded IDs.
- Removed redundant JVM/JS source map tasks, improving Gradle and Docker build consistency.
- Updated dependencies, including `logback` and Webpack `copy-webpack-plugin`, and added contextual documentation.
- Added frontend architecture diagram in PlantUML (`docs/01_Architecture/Reference`), standardizing feature-core-shell dependencies.

platform/architecture-tests/build.gradle.kts

@@ -37,7 +37,3 @@ dependencies {
   implementation(project(":frontend:core:sync"))
   implementation(project(":frontend:shells:meldestelle-portal"))
 }
-
-tasks.withType<Test>().configureEach {
-  useJUnitPlatform()
-}