feat: show timestamp on the last message of each author run

A small time label now sits in the bubble's bottom-end corner of the last
message of a group (and singles), so temporal context is always visible
without repeating it on every bubble. Hidden while the tap-to-expand
detail row is open, which already includes the time.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0129yvP2hmVeDFfuKKy94tqX

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/feed/ChatMessageCompose.kt

@@ -265,6 +265,12 @@ fun NormalChatNote(
             } else {
                 null
             },
+        timeRow =
+            if (!innerQuote && groupPosition.isLastOfGroup) {
+                { ChatTimeAgo(note) }
+            } else {
+                null
+            },
         drawAuthorLine = {
             DrawAuthorInfo(
                 note,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/feed/layouts/ChatBubbleLayout.kt

@@ -27,6 +27,7 @@ import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.combinedClickable
 import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.size
@@ -87,6 +88,9 @@ fun ChatBubbleLayout(
     onAuthorClick: () -> Unit,
     actionMenu: @Composable (onDismiss: () -> Unit) -> Unit,
     reactionsRow: (@Composable () -> Unit)? = null,
+    // Small always-visible timestamp in the bubble's bottom-end corner; skipped
+    // while the tap-to-expand detail row (which includes the time) is open.
+    timeRow: (@Composable () -> Unit)? = null,
     detailRow: @Composable () -> Unit,
     drawAuthorLine: @Composable () -> Unit,
     inner: @Composable (MutableState<Color>) -> Unit,
@@ -193,6 +197,10 @@ fun ChatBubbleLayout(
 
                     if (showDetails.value) {
                         detailRow()
+                    } else if (timeRow != null) {
+                        Box(modifier = Modifier.align(Alignment.End)) {
+                            timeRow()
+                        }
                     }
                 }
             }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/feed/layouts/ChatGroupPosition.kt

@@ -56,6 +56,9 @@ enum class ChatGroupPosition {
     val isFirstOfGroup: Boolean
         get() = this == SINGLE || this == TOP
 
+    val isLastOfGroup: Boolean
+        get() = this == SINGLE || this == BOTTOM
+
     val isConnectedAbove: Boolean
         get() = this == MIDDLE || this == BOTTOM
 }