fix: use surface color for open poll cards in dark mode notifications

The Card wrapping open polls in the notification feed was using the
default Material3 containerColor (surfaceContainerHighest), which is
too bright in dark mode where the app uses pure black backgrounds.
Explicitly set the container color to surface to match the theme.

https://claude.ai/code/session_012ErcSBhXugYCRAwHRXrFr7

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/notifications/CardFeedView.kt

@@ -35,6 +35,7 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyListState
 import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.material3.Card
+import androidx.compose.material3.CardDefaults
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
@@ -185,6 +186,7 @@ private fun FeedLoaded(
                 Row(modifier = Modifier.padding(start = Size10dp, end = Size10dp, bottom = Size10dp)) {
                     Card(
                         modifier = MaterialTheme.colorScheme.imageModifier,
+                        colors = CardDefaults.cardColors(containerColor = MaterialTheme.colorScheme.surface),
                     ) {
                         Row(
                             modifier = Modifier.fillMaxWidth(),