Added account deletion and improved login case-insensitivity

The Dashboard now includes a "Löschen" (Delete) button that allows users to remove the currently selected account via the `MainViewModel`.

The login process has been updated to convert usernames to lowercase before authentication to ensure consistency. Additionally, spacing adjustments were made to the Dashboard UI layout.

app/src/main/java/de/miaurizius/shap_planner/activities/MainActivity.kt

@@ -92,7 +92,8 @@ class MainActivity : ComponentActivity() {
                     selectedAccount != null -> {
                         DashboardScreen(
                             account = selectedAccount,
-                            onBack = { mainViewModel.logoutFromAccount() }
+                            onBack = { mainViewModel.logoutFromAccount() },
+                            onDelete = { mainViewModel.deleteAccount(selectedAccount) }
                         )
                     }
 
@@ -203,7 +204,7 @@ fun LoginScreen(onLogin: (String, String, String) -> Unit, onBack: (() -> Unit)?
 }
 
 @Composable
-fun DashboardScreen(account: Account, onBack: () -> Unit) {
+fun DashboardScreen(account: Account, onBack: () -> Unit, onDelete: () -> Unit) {
 
     BackHandler {
         onBack()
@@ -230,7 +231,13 @@ fun DashboardScreen(account: Account, onBack: () -> Unit) {
             }
         }
 
-        Spacer(modifier = Modifier.height(32.dp))
+        Spacer(modifier = Modifier.height(5.dp))
+
+        Button(onClick = onDelete) {
+            Text("Löschen")
+        }
+
+        Spacer(modifier = Modifier.height(10.dp))
 
         Box(
             modifier = Modifier

app/src/main/java/de/miaurizius/shap_planner/viewmodels/LoginViewModel.kt

@@ -13,6 +13,8 @@ import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import java.util.Locale
+import java.util.Locale.getDefault
 import java.util.UUID
 
 class LoginViewModel(private val prefs: UserPreferences, private val appContext: Context) : ViewModel() {
@@ -28,7 +30,7 @@ class LoginViewModel(private val prefs: UserPreferences, private val appContext:
 
             try {
                 val response = withContext(Dispatchers.IO) {
-                    api.login(LoginRequest(username, password))
+                    api.login(LoginRequest(username.lowercase(getDefault()), password))
                 }
 
                 if(response.isSuccessful) {

app/src/main/java/de/miaurizius/shap_planner/viewmodels/MainViewModel.kt

@@ -24,6 +24,13 @@ class MainViewModel(private val accountDao: AccountDao) : ViewModel() {
         }
     }
 
+    fun deleteAccount(account: Account) {
+        viewModelScope.launch {
+            accountDao.deleteAccount(account)
+            selectedAccount = null
+        }
+    }
+
     var selectedAccount by mutableStateOf<Account?>(null)
         private set