chore: remove obsolete screens from meldestelle-desktop module

- Deleted unused screens including `AdminUebersichtScreen`, `AktorScreens`, `StammdatenImportScreen`, `TurnierDetailScreen`, and supporting components such as `PlaceholderContent`.
- Cleaned up references and placeholders to streamline module structure.

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

frontend/features/ping-feature/src/commonMain/kotlin/at/mocode/ping/feature/presentation/PingViewModel.kt

@@ -33,13 +33,13 @@ data class PingUiState(
   val logs: List<LogEntry> = emptyList()
 )
 
-class PingViewModel(
+open class PingViewModel(
   private val apiClient: PingApi,
   private val syncService: PingSyncService
 ) : ViewModel() {
 
   var uiState by mutableStateOf(PingUiState())
-    private set
+    internal set
 
   private fun addLog(source: String, message: String, isError: Boolean = false) {
     val now = Clock.System.now().toLocalDateTime(TimeZone.currentSystemDefault())

frontend/features/ping-feature/src/jvmMain/kotlin/at/mocode/ping/feature/presentation/PingScreenPreview.kt

@@ -0,0 +1,109 @@
+package at.mocode.ping.feature.presentation
+
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.tooling.preview.Preview
+import at.mocode.ping.api.EnhancedPingResponse
+import at.mocode.ping.api.HealthResponse
+import at.mocode.ping.api.PingApi
+import at.mocode.ping.api.PingEvent
+import at.mocode.ping.api.PingResponse
+import at.mocode.ping.feature.domain.PingSyncService
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Fake-Implementierungen für Preview (kein Koin, kein Netzwerk nötig)
+// ─────────────────────────────────────────────────────────────────────────────
+
+private val fakePingResponse = PingResponse(
+  status = "OK", timestamp = "2026-03-26T12:00:00Z", service = "ping-service"
+)
+
+private val fakeEnhancedResponse = EnhancedPingResponse(
+  status = "OK", timestamp = "2026-03-26T12:00:00Z", service = "ping-service",
+  circuitBreakerState = "CLOSED", responseTime = 42L
+)
+
+private val fakeHealthResponse = HealthResponse(
+  status = "UP", timestamp = "2026-03-26T12:00:00Z", service = "ping-service", healthy = true
+)
+
+private object FakePingApi : PingApi {
+  override suspend fun simplePing() = fakePingResponse
+  override suspend fun enhancedPing(simulate: Boolean) = fakeEnhancedResponse
+  override suspend fun healthCheck() = fakeHealthResponse
+  override suspend fun publicPing() = fakePingResponse
+  override suspend fun securePing() = fakePingResponse
+  override suspend fun syncPings(since: Long): List<PingEvent> = emptyList()
+}
+
+private object FakePingSyncService : PingSyncService {
+  override suspend fun syncPings() { /* no-op */
+  }
+}
+
+// Subclass um uiState für Preview direkt setzen zu können
+private class PreviewPingViewModel(state: PingUiState) :
+  PingViewModel(FakePingApi, FakePingSyncService) {
+  init {
+    uiState = state
+  }
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Previews
+// ─────────────────────────────────────────────────────────────────────────────
+
+@Preview
+@Composable
+fun PreviewPingScreen_Empty() {
+  MaterialTheme {
+    PingScreen(
+      viewModel = PreviewPingViewModel(PingUiState()),
+      onBack = {}
+    )
+  }
+}
+
+@Preview
+@Composable
+fun PreviewPingScreen_WithData() {
+  MaterialTheme {
+    PingScreen(
+      viewModel = PreviewPingViewModel(
+        PingUiState(
+          simplePingResponse = fakePingResponse,
+          healthResponse = fakeHealthResponse,
+          logs = listOf(
+            LogEntry("12:00:01", "SimplePing", "Success: OK from ping-service"),
+            LogEntry("12:00:00", "HealthCheck", "Status: UP, Healthy: true"),
+          )
+        )
+      ),
+      onBack = {}
+    )
+  }
+}
+
+@Preview
+@Composable
+fun PreviewPingScreen_Loading() {
+  MaterialTheme {
+    PingScreen(
+      viewModel = PreviewPingViewModel(PingUiState(isLoading = true, isSyncing = true)),
+      onBack = {}
+    )
+  }
+}
+
+@Preview
+@Composable
+fun PreviewPingScreen_Error() {
+  MaterialTheme {
+    PingScreen(
+      viewModel = PreviewPingViewModel(
+        PingUiState(errorMessage = "Connection refused: Backend nicht erreichbar")
+      ),
+      onBack = {}
+    )
+  }
+}