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.

chat/components/chat.templ

@@ -23,16 +23,21 @@ type Config struct {
 	StopKeyPropagation bool
 }
 
+// ChatMessage renders a single chat message. Used for appending new messages via SSE.
+templ ChatMessage(m chat.Message, cfg Config) {
+	<div class={ cfg.CSSPrefix + "-chat-msg" }>
+		<span style={ fmt.Sprintf("color:%s;font-weight:bold;", cfg.Color(m.Slot)) }>
+			{ m.Nickname + ": " }
+		</span>
+		<span>{ m.Message }</span>
+	</div>
+}
+
 templ Chat(messages []chat.Message, cfg Config) {
 	<div id={ cfg.CSSPrefix + "-chat" } class={ cfg.CSSPrefix + "-chat" }>
-		<div class={ cfg.CSSPrefix + "-chat-history" }>
+		<div id={ cfg.CSSPrefix + "-chat-history" } class={ cfg.CSSPrefix + "-chat-history" }>
 			for _, m := range messages {
-				<div class={ cfg.CSSPrefix + "-chat-msg" }>
-					<span style={ fmt.Sprintf("color:%s;font-weight:bold;", cfg.Color(m.Slot)) }>
-						{ m.Nickname + ": " }
-					</span>
-					<span>{ m.Message }</span>
-				</div>
+				@ChatMessage(m, cfg)
 			}
 		</div>
 		<div class={ cfg.CSSPrefix + "-chat-input" } data-morph-ignore>