fix: append chat messages instead of re-rendering entire game

Previously patchAll() re-rendered the full GameContent on every chat
message, which was inefficient and could cause UI glitches. Now we
append just the new ChatMessage to the chat history element.

features/c4game/handlers.go

@@ -148,8 +148,13 @@ func HandleGameEvents(store *connect4.Store, nc *nats.Conn, sm *scs.SessionManag
 					return
 				}
 			case msg := <-chatCh:
-				room.Receive(msg.Data)
-				if err := patchAll(); err != nil {
+				chatMsg, _ := room.Receive(msg.Data)
+				err := sse.PatchElementTempl(
+					chatcomponents.ChatMessage(chatMsg, chatCfg),
+					datastar.WithSelectorID("c4-chat-history"),
+					datastar.WithModeAppend(),
+				)
+				if err != nil {
 					return
 				}
 			}