feat(item): DatePicker durch Monat/Jahr-Picker ersetzen

- Ablaufdatum wird jetzt als MM/yyyy gespeichert (letzter Tag des Monats)
- DatePickerDialog -> AlertDialog mit zwei Dropdowns (Monat, Jahr)
- Anzeige in ItemListScreen ebenfalls auf MM/yyyy umgestellt

app/src/main/java/de/krisenvorrat/app/ui/item/ItemFormScreen.kt

@@ -1,6 +1,9 @@
 package de.krisenvorrat.app.ui.item
 
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
@@ -13,8 +16,7 @@ import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.ArrowBack
 import androidx.compose.material.icons.filled.Check
 import androidx.compose.material.icons.filled.DateRange
-import androidx.compose.material3.DatePicker
-import androidx.compose.material3.DatePickerDialog
+import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.ExposedDropdownMenuBox
@@ -27,7 +29,6 @@ import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
-import androidx.compose.material3.rememberDatePickerState
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
@@ -39,9 +40,8 @@ import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.unit.dp
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
-import java.time.Instant
 import java.time.LocalDate
-import java.time.ZoneId
+import java.time.YearMonth
 import java.time.format.DateTimeFormatter
 
 @OptIn(ExperimentalMaterial3Api::class)
@@ -311,8 +311,8 @@ private fun ExpiryDateField(
     expiryDate: LocalDate?,
     onDateSelected: (LocalDate?) -> Unit
 ) {
-    var isDatePickerVisible by remember { mutableStateOf(false) }
-    val formatter = DateTimeFormatter.ofPattern("dd.MM.yyyy")
+    var isPickerVisible by remember { mutableStateOf(false) }
+    val formatter = remember { DateTimeFormatter.ofPattern("MM/yyyy") }
     val displayValue = expiryDate?.format(formatter) ?: ""
 
     OutlinedTextField(
@@ -321,51 +321,140 @@ private fun ExpiryDateField(
         readOnly = true,
         label = { Text("Ablaufdatum (MHD)") },
         trailingIcon = {
-            IconButton(onClick = { isDatePickerVisible = true }) {
+            IconButton(onClick = { isPickerVisible = true }) {
                 Icon(
                     imageVector = Icons.Default.DateRange,
                     contentDescription = "Datum wählen"
                 )
             }
         },
-        modifier = Modifier.fillMaxWidth()
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable { isPickerVisible = true }
     )
 
-    if (isDatePickerVisible) {
-        val initialMillis = expiryDate
-            ?.atStartOfDay(ZoneId.of("UTC"))
-            ?.toInstant()
-            ?.toEpochMilli()
-        val datePickerState = rememberDatePickerState(initialSelectedDateMillis = initialMillis)
+    if (isPickerVisible) {
+        MonthYearPickerDialog(
+            initialDate = expiryDate,
+            onConfirm = { yearMonth ->
+                onDateSelected(yearMonth.atEndOfMonth())
+                isPickerVisible = false
+            },
+            onRemove = {
+                onDateSelected(null)
+                isPickerVisible = false
+            },
+            onDismiss = { isPickerVisible = false }
+        )
+    }
+}
 
-        DatePickerDialog(
-            onDismissRequest = { isDatePickerVisible = false },
-            confirmButton = {
-                TextButton(
-                    onClick = {
-                        val selectedMillis = datePickerState.selectedDateMillis
-                        if (selectedMillis != null) {
-                            val selectedDate = Instant.ofEpochMilli(selectedMillis)
-                                .atZone(ZoneId.of("UTC"))
-                                .toLocalDate()
-                            onDateSelected(selectedDate)
-                        }
-                        isDatePickerVisible = false
-                    }
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+private fun MonthYearPickerDialog(
+    initialDate: LocalDate?,
+    onConfirm: (YearMonth) -> Unit,
+    onRemove: () -> Unit,
+    onDismiss: () -> Unit
 ) {
+    val today = remember { LocalDate.now() }
+    val initialYearMonth = if (initialDate != null) YearMonth.from(initialDate) else YearMonth.from(today)
+
+    var selectedMonth by remember { mutableStateOf(initialYearMonth.monthValue) }
+    var selectedYear by remember { mutableStateOf(initialYearMonth.year) }
+
+    val monthNames = remember {
+        listOf(
+            "Januar", "Februar", "März", "April", "Mai", "Juni",
+            "Juli", "August", "September", "Oktober", "November", "Dezember"
+        )
+    }
+    val years = remember(today) { (today.year - 1..today.year + 20).toList() }
+
+    var monthExpanded by remember { mutableStateOf(false) }
+    var yearExpanded by remember { mutableStateOf(false) }
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text("Ablaufdatum wählen") },
+        text = {
+            Row(
+                modifier = Modifier.fillMaxWidth(),
+                horizontalArrangement = Arrangement.spacedBy(8.dp)
+            ) {
+                ExposedDropdownMenuBox(
+                    expanded = monthExpanded,
+                    onExpandedChange = { monthExpanded = it },
+                    modifier = Modifier.weight(1f)
+                ) {
+                    OutlinedTextField(
+                        value = monthNames[selectedMonth - 1],
+                        onValueChange = {},
+                        readOnly = true,
+                        label = { Text("Monat") },
+                        trailingIcon = { ExposedDropdownMenuDefaults.TrailingIcon(expanded = monthExpanded) },
+                        modifier = Modifier.menuAnchor(MenuAnchorType.PrimaryNotEditable)
+                    )
+                    ExposedDropdownMenu(
+                        expanded = monthExpanded,
+                        onDismissRequest = { monthExpanded = false }
+                    ) {
+                        monthNames.forEachIndexed { index, name ->
+                            DropdownMenuItem(
+                                text = { Text(name) },
+                                onClick = {
+                                    selectedMonth = index + 1
+                                    monthExpanded = false
+                                }
+                            )
+                        }
+                    }
+                }
+
+                ExposedDropdownMenuBox(
+                    expanded = yearExpanded,
+                    onExpandedChange = { yearExpanded = it },
+                    modifier = Modifier.weight(1f)
+                ) {
+                    OutlinedTextField(
+                        value = selectedYear.toString(),
+                        onValueChange = {},
+                        readOnly = true,
+                        label = { Text("Jahr") },
+                        trailingIcon = { ExposedDropdownMenuDefaults.TrailingIcon(expanded = yearExpanded) },
+                        modifier = Modifier.menuAnchor(MenuAnchorType.PrimaryNotEditable)
+                    )
+                    ExposedDropdownMenu(
+                        expanded = yearExpanded,
+                        onDismissRequest = { yearExpanded = false }
+                    ) {
+                        years.forEach { year ->
+                            DropdownMenuItem(
+                                text = { Text(year.toString()) },
+                                onClick = {
+                                    selectedYear = year
+                                    yearExpanded = false
+                                }
+                            )
+                        }
+                    }
+                }
+            }
+        },
+        confirmButton = {
+            TextButton(onClick = { onConfirm(YearMonth.of(selectedYear, selectedMonth)) }) {
                 Text("OK")
             }
         },
         dismissButton = {
-                TextButton(onClick = {
-                    onDateSelected(null)
-                    isDatePickerVisible = false
-                }) {
+            Row {
+                TextButton(onClick = onRemove) {
                     Text("Entfernen")
                 }
-            }
-        ) {
-            DatePicker(state = datePickerState)
+                TextButton(onClick = onDismiss) {
+                    Text("Abbrechen")
                 }
             }
         }
+    )
+}

app/src/main/java/de/krisenvorrat/app/ui/item/ItemListScreen.kt

@@ -33,6 +33,7 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -231,18 +232,14 @@ private fun ItemCard(
 
 @Composable
 private fun ExpiryDateText(item: ItemUiModel) {
-    val formatter = DateTimeFormatter.ofPattern("dd.MM.yyyy")
+    val formatter = remember { DateTimeFormatter.ofPattern("MM/yyyy") }
     val formattedDate = item.expiryDate?.format(formatter).orEmpty()
     val color = when {
         item.isExpired -> MaterialTheme.colorScheme.error
         item.isExpiringSoon -> MaterialTheme.colorScheme.tertiary
         else -> MaterialTheme.colorScheme.onSurfaceVariant
     }
-    val prefix = when {
-        item.isExpired -> "Abgelaufen: "
-        item.isExpiringSoon -> "MHD: "
-        else -> "MHD: "
-    }
+    val prefix = if (item.isExpired) "Abgelaufen: " else "MHD: "
     Text(
         text = "$prefix$formattedDate",
         style = MaterialTheme.typography.bodySmall,