feat: add RemoveHidden option to strip display:none elements before extraction

When RemoveHidden is true, JavaScript is evaluated on the live page to
remove all elements with computed display:none before readability
extraction. This defends against anti-scraping honeypots that embed
prompt injections in hidden DOM elements.

The implementation uses an optional pageEvaluator interface so that the
concrete document (backed by Playwright) supports it while the Document
interface remains unchanged.

Closes #62

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

document.go

@@ -68,6 +68,10 @@ func (d *document) Refresh() error {
 	return nil
 }
 
+func (d *document) PageEvaluate(expression string) (interface{}, error) {
+	return d.page.Evaluate(expression)
+}
+
 func (d *document) WaitForNetworkIdle(timeout *time.Duration) error {
 	if timeout == nil {
 		t := 30 * time.Second