feat: add PromoteToInteractive and DemoteToDocument for mid-session page transfer

Allow transferring ownership of a Playwright page between Document and
InteractiveBrowser modes without tearing down the browser. This enables
handing a live page to a human (e.g. for captcha solving) and resuming
scraping on the same page afterward.

Closes #76

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

document.go

@@ -22,9 +22,10 @@ type Document interface {
 
 type document struct {
 	node
-	pw      *playwright.Playwright
-	browser playwright.Browser
-	page    playwright.Page
+	pw       *playwright.Playwright
+	browser  playwright.Browser
+	page     playwright.Page
+	detached bool
 }
 
 func newDocument(pw *playwright.Playwright, browser playwright.Browser, page playwright.Page) (Document, error) {
@@ -44,6 +45,9 @@ func newDocument(pw *playwright.Playwright, browser playwright.Browser, page pla
 	return res, nil
 }
 func (d *document) Close() error {
+	if d.detached {
+		return nil
+	}
 	return d.page.Close()
 }