feat(management-feature): add centralized administration screens and back-navigation support

- Introduced comprehensive management screens for horses, riders, clubs, and officials.
- Integrated reusable `ManagementTableScreen` component for standardized layouts and operations.
- Added back-navigation support in `DesktopNavigationPort` with a stack-based implementation.
- Refined `DesktopMainLayout` with enhanced routing and dynamic placeholders for in-development screens.
- Updated roadmap to reflect completion of Phase 7: "Zentrale Verwaltung".

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

frontend/features/zns-import-feature/src/jvmMain/kotlin/at/mocode/zns/feature/presentation/StammdatenImportScreen.kt

@@ -6,6 +6,7 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import androidx.compose.material.icons.filled.*
 import androidx.compose.material3.*
 import androidx.compose.runtime.Composable
@@ -21,6 +22,7 @@ import javax.swing.filechooser.FileNameExtensionFilter
 @Composable
 fun StammdatenImportScreen(
   viewModel: ZnsImportViewModel = koinViewModel(),
+  onBack: () -> Unit,
 ) {
   val state = viewModel.state
 
@@ -32,6 +34,9 @@ fun StammdatenImportScreen(
   ) {
     // Titel
     Row(verticalAlignment = Alignment.CenterVertically, horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+      IconButton(onClick = onBack) {
+        Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Zurück")
+      }
       Icon(Icons.Default.CloudUpload, contentDescription = null, tint = MaterialTheme.colorScheme.primary)
       Text("Stammdaten-Import (ZNS)", style = MaterialTheme.typography.headlineSmall)
     }