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/shells/meldestelle-desktop/build.gradle.kts

@@ -29,6 +29,7 @@ kotlin {
       // Feature-Module
       implementation(projects.frontend.features.nennungFeature)
       implementation(projects.frontend.features.pingFeature)
+      implementation(projects.frontend.features.znsImportFeature)
 
       // Compose Desktop
       implementation(compose.desktop.currentOs)