fix(feedback): show the operator reply only on the player's latest message

A reply was bound to 'the latest message that has a reply', so after the player
read a reply and sent a new (unanswered) message, the old reply kept showing as
'Ответ на ваше последнее сообщение'. Bind it to the single most-recent message
instead: sending any new message immediately drops the previous reply (the new
message has no reply yet), well before the one-week window. Client clears the
reply optimistically on submit; the mock mirrors it; inttest covers the case.

backend/internal/inttest/feedback_test.go

@@ -110,6 +110,41 @@ func TestFeedbackSubmitGateAndReplyLifecycle(t *testing.T) {
 	}
 }
 
+func TestFeedbackReplyHiddenAfterNewMessage(t *testing.T) {
+	ctx := context.Background()
+	svc := newFeedbackService()
+	acc := provisionAccount(t)
+
+	// msg1, replied → the player can send again and currently sees the reply.
+	if err := svc.Submit(ctx, acc, "first", nil, "", "web", ""); err != nil {
+		t.Fatalf("submit msg1: %v", err)
+	}
+	if err := svc.Reply(ctx, latestFeedbackID(t, svc, acc), "the answer"); err != nil {
+		t.Fatalf("reply: %v", err)
+	}
+	if st, err := svc.State(ctx, acc); err != nil {
+		t.Fatal(err)
+	} else if st.Reply == nil || st.Reply.Body != "the answer" {
+		t.Fatalf("reply not shown before the new message: %+v", st.Reply)
+	}
+
+	// Sending a new message immediately drops the previous reply (it now belongs to an
+	// older message), even though it is well within the one-week window.
+	if err := svc.Submit(ctx, acc, "second", nil, "", "web", ""); err != nil {
+		t.Fatalf("submit msg2: %v", err)
+	}
+	st, err := svc.State(ctx, acc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if st.Reply != nil {
+		t.Fatalf("reply should be hidden after a new message, got %+v", st.Reply)
+	}
+	if st.CanSend || st.BlockedReason != "pending" {
+		t.Fatalf("state after new message = %+v, want pending", st)
+	}
+}
+
 func TestFeedbackBanRole(t *testing.T) {
 	ctx := context.Background()
 	svc := newFeedbackService()