Fix: Explicitly set Top arrangement for PhotoReasoningScreen main Column

To further address issues with status cards appearing "in the middle",
this commit explicitly sets `verticalArrangement = Arrangement.Top`
on the main `Column` within `PhotoReasoningScreen.kt`.

Combined with `fillMaxHeight()` on this Column and `weight(1f)`
on the chat message `LazyColumn`, this aims to ensure that all
elements are laid out from the top and that the status cards are
pushed to the bottom of the screen.

Author: google-labs-jules[bot]

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/PhotoReasoningScreen.kt

@@ -273,7 +273,10 @@ fun PhotoReasoningScreen(
         }
     }
 
-    Column(modifier = Modifier.padding(all = 16.dp).fillMaxHeight()) {
+    Column(
+        modifier = Modifier.padding(all = 16.dp).fillMaxHeight(),
+        verticalArrangement = Arrangement.Top
+    ) {
         Card(
             modifier = Modifier.fillMaxWidth().padding(bottom = 16.dp),
             colors = CardDefaults.cardColors(containerColor = MaterialTheme.colorScheme.primaryContainer)