auth: save cookies after resp

Cookies could be expired, so we save them if we have them

auth/client.go

···
 	return &http.Client{Jar: jar}, nil
 }
 
-// saveCookies serializes the cookies and saves them to the system keyring
-func saveCookies(cookies []*http.Cookie, host string, handle string) error {
+// SaveCookies serializes the cookies and saves them to the system keyring
+func SaveCookies(cookies []*http.Cookie, host string, handle string) error {
+	if len(cookies) == 0 {
+		return nil
+	}
 	data, err := json.Marshal(cookies)
 	if err != nil {
 		return err

auth/login.go

···
 		return fmt.Errorf("authenticating: %w", err)
 	}
 
-	if err := saveCookies(cookies, "tangled.sh", handle); err != nil {
+	if err := SaveCookies(cookies, knit.DefaultHost, handle); err != nil {
 		return err
 	}
 

pr/create.go

···
 		return err
 	}
 	defer resp.Body.Close()
+	auth.SaveCookies(resp.Cookies(), knit.DefaultHost, handle)
 
 	if resp.StatusCode != http.StatusOK {
 		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
···
 
 	stop()
 	wg.Wait()
+	fmt.Printf("\x1b[32m✔\x1b[m  PR created!\r\n")
 
 	return nil
 }