refactor(auth): migrate Auth module from feature to core package

- Reorganized `auth-feature` into `core/auth` to improve architecture and modularity.
- Removed unused PKCE and OAuth callback utilities (`AuthCallbackParams`, `OAuthPkceService`).
- Updated imports and adjusted build scripts to reflect new module structure.
- Refactored `LoginScreen` and `PingScreen` to include `onBack` functionality in top bars for improved navigation.
- Corrected sync endpoint in `PingSyncService`.

frontend/features/ping-feature/src/commonMain/kotlin/at/mocode/ping/feature/domain/PingSyncService.kt

@@ -20,6 +20,7 @@ class PingSyncServiceImpl(
 ) : PingSyncService {
 
   override suspend fun syncPings() {
-    syncManager.performSync(repository, "/api/pings/sync")
+    // Corrected endpoint: /api/ping/sync (singular)
+    syncManager.performSync(repository, "/api/ping/sync")
   }
 }

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

@@ -8,121 +8,131 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
-import androidx.compose.material3.Button
-import androidx.compose.material3.Card
-import androidx.compose.material3.CircularProgressIndicator
-import androidx.compose.material3.MaterialTheme
-import androidx.compose.material3.Text
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material3.*
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 
+@OptIn(ExperimentalMaterial3Api::class)
 @Composable
-fun PingScreen(viewModel: PingViewModel) {
+fun PingScreen(
+  viewModel: PingViewModel,
+  onBack: () -> Unit = {}
+) {
   val uiState = viewModel.uiState
   val scrollState = rememberScrollState()
 
-  Column(
-    modifier = Modifier
-      .fillMaxSize()
-      .padding(16.dp)
-      .verticalScroll(scrollState),
-    verticalArrangement = Arrangement.spacedBy(16.dp)
-  ) {
-    Text(
-      text = "Ping Service",
-      style = MaterialTheme.typography.headlineMedium,
-      fontWeight = FontWeight.Bold
-    )
-
-    if (uiState.isLoading || uiState.isSyncing) {
-      CircularProgressIndicator()
+  Scaffold(
+    topBar = {
+      TopAppBar(
+        title = { Text("Ping Service") },
+        navigationIcon = {
+          IconButton(onClick = onBack) {
+            Icon(Icons.AutoMirrored.Filled.ArrowBack, contentDescription = "Zurück")
+          }
+        }
+      )
     }
+  ) { paddingValues ->
+    Column(
+      modifier = Modifier
+        .fillMaxSize()
+        .padding(paddingValues)
+        .padding(16.dp)
+        .verticalScroll(scrollState),
+      verticalArrangement = Arrangement.spacedBy(16.dp)
+    ) {
+      if (uiState.isLoading || uiState.isSyncing) {
+        CircularProgressIndicator()
+      }
 
-    if (uiState.errorMessage != null) {
-      Card(modifier = Modifier.fillMaxWidth()) {
-        Column(modifier = Modifier.padding(16.dp)) {
-          Text(
-            text = "Error",
-            style = MaterialTheme.typography.titleMedium,
-            color = MaterialTheme.colorScheme.error
-          )
-          Text(text = uiState.errorMessage)
-          Button(onClick = { viewModel.clearError() }) {
-            Text("Clear")
+      if (uiState.errorMessage != null) {
+        Card(modifier = Modifier.fillMaxWidth()) {
+          Column(modifier = Modifier.padding(16.dp)) {
+            Text(
+              text = "Error",
+              style = MaterialTheme.typography.titleMedium,
+              color = MaterialTheme.colorScheme.error
+            )
+            Text(text = uiState.errorMessage)
+            Button(onClick = { viewModel.clearError() }) {
+              Text("Clear")
+            }
           }
         }
       }
-    }
 
-    if (uiState.lastSyncResult != null) {
-      Card(modifier = Modifier.fillMaxWidth()) {
-        Column(modifier = Modifier.padding(16.dp)) {
-          Text(
-            text = "Sync Status",
-            style = MaterialTheme.typography.titleMedium,
-            color = MaterialTheme.colorScheme.primary
-          )
-          Text(text = uiState.lastSyncResult)
+      if (uiState.lastSyncResult != null) {
+        Card(modifier = Modifier.fillMaxWidth()) {
+          Column(modifier = Modifier.padding(16.dp)) {
+            Text(
+              text = "Sync Status",
+              style = MaterialTheme.typography.titleMedium,
+              color = MaterialTheme.colorScheme.primary
+            )
+            Text(text = uiState.lastSyncResult)
+          }
         }
       }
-    }
 
-    Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
-      Button(onClick = { viewModel.performSimplePing() }) {
-        Text("Simple Ping")
-      }
-      Button(onClick = { viewModel.performEnhancedPing() }) {
-        Text("Enhanced Ping")
-      }
-    }
-
-    Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
-      Button(onClick = { viewModel.performHealthCheck() }) {
-        Text("Health Check")
-      }
-      Button(onClick = { viewModel.performSecurePing() }) {
-        Text("Secure Ping")
-      }
-    }
-
-    Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
-      Button(onClick = { viewModel.triggerSync() }) {
-        Text("Sync Now")
-      }
-    }
-
-    if (uiState.simplePingResponse != null) {
-      Card(modifier = Modifier.fillMaxWidth()) {
-        Column(modifier = Modifier.padding(16.dp)) {
-          Text("Simple / Secure Ping Response:", style = MaterialTheme.typography.titleMedium)
-          Text("Status: ${uiState.simplePingResponse.status}")
-          Text("Service: ${uiState.simplePingResponse.service}")
-          Text("Timestamp: ${uiState.simplePingResponse.timestamp}")
+      Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+        Button(onClick = { viewModel.performSimplePing() }) {
+          Text("Simple Ping")
+        }
+        Button(onClick = { viewModel.performEnhancedPing() }) {
+          Text("Enhanced Ping")
         }
       }
-    }
 
-    if (uiState.enhancedPingResponse != null) {
-      Card(modifier = Modifier.fillMaxWidth()) {
-        Column(modifier = Modifier.padding(16.dp)) {
-          Text("Enhanced Ping Response:", style = MaterialTheme.typography.titleMedium)
-          Text("Status: ${uiState.enhancedPingResponse.status}")
-          Text("Timestamp: ${uiState.enhancedPingResponse.timestamp}")
-          Text("Circuit Breaker: ${uiState.enhancedPingResponse.circuitBreakerState}")
-          Text("Response Time: ${uiState.enhancedPingResponse.responseTime}ms")
+      Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+        Button(onClick = { viewModel.performHealthCheck() }) {
+          Text("Health Check")
+        }
+        Button(onClick = { viewModel.performSecurePing() }) {
+          Text("Secure Ping")
         }
       }
-    }
 
-    if (uiState.healthResponse != null) {
-      Card(modifier = Modifier.fillMaxWidth()) {
-        Column(modifier = Modifier.padding(16.dp)) {
-          Text("Health Response:", style = MaterialTheme.typography.titleMedium)
-          Text("Status: ${uiState.healthResponse.status}")
-          Text("Healthy: ${uiState.healthResponse.healthy}")
-          Text("Service: ${uiState.healthResponse.service}")
+      Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+        Button(onClick = { viewModel.triggerSync() }) {
+          Text("Sync Now")
+        }
+      }
+
+      if (uiState.simplePingResponse != null) {
+        Card(modifier = Modifier.fillMaxWidth()) {
+          Column(modifier = Modifier.padding(16.dp)) {
+            Text("Simple / Secure Ping Response:", style = MaterialTheme.typography.titleMedium)
+            Text("Status: ${uiState.simplePingResponse.status}")
+            Text("Service: ${uiState.simplePingResponse.service}")
+            Text("Timestamp: ${uiState.simplePingResponse.timestamp}")
+          }
+        }
+      }
+
+      if (uiState.enhancedPingResponse != null) {
+        Card(modifier = Modifier.fillMaxWidth()) {
+          Column(modifier = Modifier.padding(16.dp)) {
+            Text("Enhanced Ping Response:", style = MaterialTheme.typography.titleMedium)
+            Text("Status: ${uiState.enhancedPingResponse.status}")
+            Text("Timestamp: ${uiState.enhancedPingResponse.timestamp}")
+            Text("Circuit Breaker: ${uiState.enhancedPingResponse.circuitBreakerState}")
+            Text("Response Time: ${uiState.enhancedPingResponse.responseTime}ms")
+          }
+        }
+      }
+
+      if (uiState.healthResponse != null) {
+        Card(modifier = Modifier.fillMaxWidth()) {
+          Column(modifier = Modifier.padding(16.dp)) {
+            Text("Health Response:", style = MaterialTheme.typography.titleMedium)
+            Text("Status: ${uiState.healthResponse.status}")
+            Text("Healthy: ${uiState.healthResponse.healthy}")
+            Text("Service: ${uiState.healthResponse.service}")
+          }
         }
       }
     }