chore: remove unused meldestelle-portal module

- Deleted obsolete `meldestelle-portal` module, including all associated screens, configurations, tests, and assets.
- Includes removal of Compose multiplatform dependencies in `build.gradle.kts`.
- Cleaned up redundant files such as `AppPreview`, `AuthStatusScreen`, `DashboardScreen`, and associated core implementations.
- Streamlined module references in `settings.gradle.kts`.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

frontend/core/navigation/build.gradle.kts

@@ -23,6 +23,7 @@ kotlin {
     commonMain.dependencies {
       // Depend on core domain for User/Role types used by navigation API
       implementation(projects.frontend.core.domain)
+      implementation(libs.kotlinx.coroutines.core)
     }
     commonTest.dependencies {
       implementation(libs.kotlin.test)