fix(op): initialize http Headers in response objects

pkg/op/server.go

@@ -218,6 +218,7 @@ type Response struct {
 // without custom headers.
 func NewResponse(data any) *Response {
 	return &Response{
+		Header: make(http.Header),
 		Data:   data,
 	}
 }
@@ -242,7 +243,10 @@ type Redirect struct {
 }
 
 func NewRedirect(url string) *Redirect {
-	return &Redirect{URL: url}
+	return &Redirect{
+		Header: make(http.Header),
+		URL:    url,
+	}
 }
 
 func (red *Redirect) writeOut(w http.ResponseWriter, r *http.Request) {