fix(mutual): gate prefill scroll on real list layout (onGloballyPositioned)

On a device the Mutual entry is composed inside the NavDisplay transition;
LaunchedEffect could run before the LazyColumn is measurable and the
scrollToItem then never lands, leaving the page at the top. Only scroll
once onGloballyPositioned confirms the list has actually been laid out.

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualScreen.kt

@@ -54,11 +54,13 @@ import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.layout.onGloballyPositioned
 import androidx.compose.ui.res.painterResource
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontWeight
@@ -220,8 +222,18 @@ private fun MutualContent(
             }
     }
 
+    // Set once the list has actually been laid out. The prefill scroll only
+    // fires after this, because on a real device the Mutual entry appears
+    // through the NavDisplay transition and LaunchedEffect alone can run
+    // before the list is measurable (the scroll then never lands and the
+    // page stays at the top). onGloballyPositioned fires on the first real
+    // layout, so the subsequent scrollToItem always has a measured list.
+    var listReady by remember { mutableStateOf(false) }
+
     LazyColumn(
-        modifier = Modifier.fillMaxSize(),
+        modifier = Modifier
+            .fillMaxSize()
+            .onGloballyPositioned { listReady = true },
         state = listState,
         verticalArrangement = Arrangement.spacedBy(6.dp)
     ) {
@@ -377,8 +389,8 @@ private fun MutualContent(
     // LazyListState at index 1: the constructor parameter is ignored by this
     // Compose version (verified in tests), while scrollToItem lands correctly.
     val matchSearchIndex = if (state.errorMessage != null) 2 else 1
-    LaunchedEffect(state.scrollToTimeRange, matchSearchIndex) {
+    LaunchedEffect(state.scrollToTimeRange, matchSearchIndex, listReady) {
-        if (state.scrollToTimeRange) {
+        if (state.scrollToTimeRange && listReady) {
             listState.scrollToItem(matchSearchIndex)
             viewModel.consumeScrollToTimeRange()
         }