perf: avoid O(N^2) indexOf in notifications list

Replace items(...) + notifications.indexOf(item) with itemsIndexed(...)
in NotificationsScreen. The indexOf call ran during composition for
every visible item, causing a linear scan per item and quadratic total
work as the list grew. Reported as a UI freeze when tapping the
notifications tab on slower devices (GrapheneOS).

app/src/main/kotlin/com/wisp/app/ui/screen/NotificationsScreen.kt

@@ -22,6 +22,7 @@ import androidx.compose.foundation.layout.widthIn
 import androidx.compose.foundation.layout.wrapContentSize
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
@@ -381,9 +382,9 @@ fun NotificationsScreen(
                         }
                     )
                 }
-                items(items = notifications, key = { it.id }, contentType = { "notification" }) { item ->
+                itemsIndexed(items = notifications, key = { _, it -> it.id }, contentType = { _, _ -> "notification" }) { index, item ->
                     val isExpanded = expandedId == item.id
-                    val itemIndex = notifications.indexOf(item) + 1 // +1 for summary header
+                    val itemIndex = index + 1 // +1 for summary header
                     val coroutineScope = rememberCoroutineScope()
                     ZenNotificationRow(
                         item = item,