feat: add call buttons to group chat header

Adds voice and video call buttons to the group DM top bar, matching
the existing 1-on-1 DM header.  When tapped in a group chat, the
buttons invoke initiateGroupCall() which sends gift-wrapped offers
to every group member under a single call-id.

https://claude.ai/code/session_01WafqMofFQfWCQA5TcLvHRb

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/privateDM/ChatroomScreen.kt

@@ -49,18 +49,27 @@ fun ChatroomScreen(
     nav: INav,
 ) {
     val context = LocalContext.current
+    val isGroupChat = roomId.users.size > 1
     val startVoiceCall =
         rememberCallWithPermission(context) {
-            val peerPubKey = roomId.users.firstOrNull() ?: return@rememberCallWithPermission
             ActiveCallHolder.set(accountViewModel.callManager, accountViewModel.callController, accountViewModel)
+            if (isGroupChat) {
+                accountViewModel.callController?.initiateGroupCall(roomId.users.toSet(), CallType.VOICE)
+            } else {
+                val peerPubKey = roomId.users.firstOrNull() ?: return@rememberCallWithPermission
                 accountViewModel.callController?.initiateCall(peerPubKey, CallType.VOICE)
+            }
             CallActivity.launch(context)
         }
     val startVideoCall =
         rememberCallWithPermission(context, isVideo = true) {
-            val peerPubKey = roomId.users.firstOrNull() ?: return@rememberCallWithPermission
             ActiveCallHolder.set(accountViewModel.callManager, accountViewModel.callController, accountViewModel)
+            if (isGroupChat) {
+                accountViewModel.callController?.initiateGroupCall(roomId.users.toSet(), CallType.VIDEO)
+            } else {
+                val peerPubKey = roomId.users.firstOrNull() ?: return@rememberCallWithPermission
                 accountViewModel.callController?.initiateCall(peerPubKey, CallType.VIDEO)
+            }
             CallActivity.launch(context)
         }
 

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/privateDM/header/RenderRoomTopBar.kt

@@ -146,6 +146,34 @@ fun RenderRoomTopBar(
                     )
 
                     RoomNameOnlyDisplay(room, Modifier.padding(start = 10.dp).weight(1f), FontWeight.Normal, accountViewModel)
+
+                    if (onVideoCallClick != null) {
+                        IconButton(
+                            onClick = { onVideoCallClick(room.users.joinToString(",")) },
+                            modifier = Modifier.size(40.dp),
+                        ) {
+                            Icon(
+                                imageVector = Icons.Default.Videocam,
+                                contentDescription = stringRes(R.string.call_video),
+                                tint = MaterialTheme.colorScheme.primary,
+                                modifier = Modifier.size(20.dp),
+                            )
+                        }
+                    }
+
+                    if (onCallClick != null) {
+                        IconButton(
+                            onClick = { onCallClick(room.users.joinToString(",")) },
+                            modifier = Modifier.size(40.dp),
+                        ) {
+                            Icon(
+                                imageVector = Icons.Default.Call,
+                                contentDescription = stringRes(R.string.call_voice),
+                                tint = MaterialTheme.colorScheme.primary,
+                                modifier = Modifier.size(20.dp),
+                            )
+                        }
+                    }
                 }
             },
             extendableRow = {