feat: keep Public Chats scrolled to top when new top items arrive

When the first item of either the pinned or unpinned block changes,
animate-scroll back to index 0 if the user was at or near the very top.
This mirrors the pattern from ChatFeedView so a new chat bubbling up
doesn't leave the user one row below it.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/publicChats/PublicChatsFeedLoaded.kt

@@ -35,6 +35,7 @@ import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
@@ -77,6 +78,12 @@ fun PublicChatsFeedLoaded(
             items.list.filter { it.idHex !in followedSet }
         }
 
+    LaunchedEffect(pinned.firstOrNull()?.idHex, unpinned.firstOrNull()?.idHex) {
+        if (listState.firstVisibleItemIndex <= 1) {
+            listState.animateScrollToItem(0)
+        }
+    }
+
     LazyColumn(
         contentPadding = rememberFeedContentPadding(FeedPadding),
         state = listState,