Fix: Restore main Column layout in PhotoReasoningScreen

This commit restores `Modifier.fillMaxHeight()` and explicit
`verticalArrangement = Arrangement.Top` to the main `Column`
in `PhotoReasoningScreen.kt`.

The order of elements within this Column has been previously
verified to be correct, with the `LazyColumn` for chat messages
using `Modifier.weight(1f)` and the status cards' `Column`
being the last major UI element.

This configuration is the standard way to ensure footer elements
are pushed to the bottom of a full-height screen.

Author: google-labs-jules[bot]

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

@@ -274,7 +274,8 @@ fun PhotoReasoningScreen(
     }
 
     Column(
-        modifier = Modifier.padding(all = 16.dp)
+        modifier = Modifier.padding(all = 16.dp).fillMaxHeight(),
+        verticalArrangement = Arrangement.Top
     ) {
         Card(
             modifier = Modifier.fillMaxWidth().padding(bottom = 16.dp),