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/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/AppFooter.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.*

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/AppHeader.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 import androidx.compose.material3.*
 import androidx.compose.runtime.Composable

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/AppScaffold.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 import androidx.compose.foundation.layout.PaddingValues
 import androidx.compose.foundation.layout.fillMaxSize

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/LoadingIndicator.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 import androidx.compose.foundation.layout.*
 import androidx.compose.material3.*

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/MeldestelleButton.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/MeldestelleTextField.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.fillMaxWidth

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/components/NotificationCard.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.components
+package at.mocode.frontend.core.designsystem.components
 
 // Legacy notification components removed due to dependency on old presentation layer.
 // Intentionally left empty as part of cleanup. You can safely delete this file

frontend/core/design-system/src/commonMain/kotlin/at/mocode/frontend/core/designsystem/theme/AppTheme.kt

@@ -1,4 +1,4 @@
-package at.mocode.clients.shared.commonui.theme
+package at.mocode.frontend.core.designsystem.theme
 
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.darkColorScheme