fix: add nil guards to prevent nil-pointer panics

- document.go: check if resp is nil before calling resp.Status() in
  Refresh(), since Playwright's Reload() can return a nil response
- archive.go: check SelectFirst() results for nil before calling
  Type() and Click(), preventing panics when DOM elements are missing

Closes #10, #11

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

document.go

@@ -61,7 +61,7 @@ func (d *document) Refresh() error {
 		return fmt.Errorf("failed to reload page: %w", err)
 	}
 
-	if resp.Status() != 200 {
+	if resp != nil && resp.Status() != 200 {
 		return fmt.Errorf("invalid status code: %d", resp.Status())
 	}