feat: add connection status indicator with SSE heartbeat

- Add ConnectionIndicator component showing green/red dot
- Send lastPing signal every 15 seconds via SSE
- Indicator turns red if no ping received in 20 seconds
- Gives users confidence the live connection is active

chat/chat.go

@@ -76,12 +76,11 @@ func (r *Room) Send(msg Message) {
 	}
 }
 
-// Receive processes an incoming NATS message, appending it to the buffer.
-// Returns the new message and a snapshot of all messages.
-func (r *Room) Receive(data []byte) (Message, []Message) {
+// receive processes an incoming NATS message, appending it to the buffer.
+func (r *Room) receive(data []byte) (Message, bool) {
 	var msg Message
 	if err := json.Unmarshal(data, &msg); err != nil {
-		return msg, nil
+		return msg, false
 	}
 
 	r.mu.Lock()
@@ -89,11 +88,9 @@ func (r *Room) Receive(data []byte) (Message, []Message) {
 	if len(r.messages) > maxMessages {
 		r.messages = r.messages[len(r.messages)-maxMessages:]
 	}
-	snapshot := make([]Message, len(r.messages))
-	copy(snapshot, r.messages)
 	r.mu.Unlock()
 
-	return msg, snapshot
+	return msg, true
 }
 
 // Messages returns a snapshot of the current message buffer.
@@ -105,15 +102,32 @@ func (r *Room) Messages() []Message {
 	return snapshot
 }
 
-// Subscribe creates a NATS channel subscription for the room's subject.
-// Caller is responsible for unsubscribing.
-func (r *Room) Subscribe() (chan *nats.Msg, *nats.Subscription, error) {
-	ch := make(chan *nats.Msg, 64)
-	sub, err := r.nc.ChanSubscribe(r.subject, ch)
+// Subscribe returns a channel of parsed messages and a cleanup function.
+// The room handles NATS subscription internally and buffers messages.
+func (r *Room) Subscribe() (<-chan Message, func()) {
+	natsCh := make(chan *nats.Msg, 64)
+	msgCh := make(chan Message, 64)
+
+	sub, err := r.nc.ChanSubscribe(r.subject, natsCh)
 	if err != nil {
-		return nil, nil, err
+		close(msgCh)
+		return msgCh, func() {}
 	}
-	return ch, sub, nil
+
+	go func() {
+		for natsMsg := range natsCh {
+			if msg, ok := r.receive(natsMsg.Data); ok {
+				msgCh <- msg
+			}
+		}
+		close(msgCh)
+	}()
+
+	cleanup := func() {
+		_ = sub.Unsubscribe()
+	}
+
+	return msgCh, cleanup
 }
 
 func (r *Room) saveMessage(msg Message) {

features/c4game/handlers.go

@@ -142,11 +142,8 @@ func HandleGameEvents(store *connect4.Store, nc *nats.Conn, sm *scs.SessionManag
 		defer gameSub.Unsubscribe() //nolint:errcheck
 
 		// Subscribe to chat messages
-		chatCh, chatSub, err := room.Subscribe()
-		if err != nil {
-			return
-		}
-		defer chatSub.Unsubscribe() //nolint:errcheck
+		chatCh, cleanupChat := room.Subscribe()
+		defer cleanupChat()
 
 		ctx := r.Context()
 		for {
@@ -161,8 +158,7 @@ func HandleGameEvents(store *connect4.Store, nc *nats.Conn, sm *scs.SessionManag
 				if err := patchAll(); err != nil {
 					return
 				}
-			case msg := <-chatCh:
-				chatMsg, _ := room.Receive(msg.Data)
+			case chatMsg := <-chatCh:
 				err := sse.PatchElementTempl(
 					chatcomponents.ChatMessage(chatMsg, chatCfg),
 					datastar.WithSelectorID("c4-chat-history"),

features/snakegame/handlers.go

@@ -148,15 +148,12 @@ func HandleSnakeEvents(snakeStore *snake.SnakeStore, nc *nats.Conn, sm *scs.Sess
 		defer gameSub.Unsubscribe() //nolint:errcheck
 
 		// Chat subscription (multiplayer only)
-		var chatCh chan *nats.Msg
-		var chatSub *nats.Subscription
+		var chatCh <-chan chat.Message
+		var cleanupChat func()
 
 		if room != nil {
-			chatCh, chatSub, err = room.Subscribe()
-			if err != nil {
-				return
-			}
-			defer chatSub.Unsubscribe() //nolint:errcheck
+			chatCh, cleanupChat = room.Subscribe()
+			defer cleanupChat()
 		}
 
 		ctx := r.Context()
@@ -184,11 +181,10 @@ func HandleSnakeEvents(snakeStore *snake.SnakeStore, nc *nats.Conn, sm *scs.Sess
 					return
 				}
 
-			case msg := <-chatCh:
-				if msg == nil {
+			case chatMsg, ok := <-chatCh:
+				if !ok {
 					continue
 				}
-				chatMsg, _ := room.Receive(msg.Data)
 				err := sse.PatchElementTempl(
 					chatcomponents.ChatMessage(chatMsg, chatCfg),
 					datastar.WithSelectorID("snake-chat-history"),