refactor(ui): replace Divider with HorizontalDivider in NennungsMaske for consistent styling and updated imports

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

frontend/shells/meldestelle-portal/src/commonMain/kotlin/MainApp.kt

@@ -1,6 +1,8 @@
 import androidx.compose.foundation.layout.*
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import androidx.compose.material3.*
 import androidx.compose.runtime.*
 import androidx.compose.ui.Alignment
@@ -9,8 +11,6 @@ import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
-import androidx.compose.material.icons.Icons
-import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import at.mocode.frontend.core.auth.data.AuthTokenManager
 import at.mocode.frontend.core.auth.presentation.LoginScreen
 import at.mocode.frontend.core.auth.presentation.LoginViewModel
@@ -1316,7 +1316,7 @@ private fun OrganizerProfileScreen(
             onValueChange = { vereinsname = it },
             label = { Text("Vereinsname / Veranstalter") },
             singleLine = true,
-            modifier = androidx.compose.ui.Modifier.fillMaxWidth()
+            modifier = Modifier.fillMaxWidth()
           )
           OutlinedTextField(
             value = vereinskuerzel,