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>

interactive.go

@@ -48,10 +48,12 @@ type InteractiveBrowser interface {
 }
 
 type interactiveBrowser struct {
-	pw      *playwright.Playwright
-	browser playwright.Browser
-	ctx     playwright.BrowserContext
-	page    playwright.Page
+	pw                 *playwright.Playwright
+	browser            playwright.Browser
+	ctx                playwright.BrowserContext
+	page               playwright.Page
+	ownsInfrastructure bool
+	detached           bool
 }
 
 // NewInteractiveBrowser creates a headless browser with a page ready for interactive control.
@@ -94,10 +96,11 @@ func NewInteractiveBrowser(ctx context.Context, opts ...BrowserOptions) (Interac
 
 		ch <- result{
 			ib: &interactiveBrowser{
-				pw:      res.pw,
-				browser: res.browser,
-				ctx:     res.bctx,
-				page:    page,
+				pw:                 res.pw,
+				browser:            res.browser,
+				ctx:                res.bctx,
+				page:               page,
+				ownsInfrastructure: true,
 			},
 		}
 	}()
@@ -194,25 +197,31 @@ func (ib *interactiveBrowser) Cookies() ([]Cookie, error) {
 }
 
 func (ib *interactiveBrowser) Close() error {
+	if ib.detached {
+		return nil
+	}
+
 	var errs []error
 	if ib.page != nil {
 		if err := ib.page.Close(); err != nil {
 			errs = append(errs, err)
 		}
 	}
-	if ib.ctx != nil {
-		if err := ib.ctx.Close(); err != nil {
-			errs = append(errs, err)
+	if ib.ownsInfrastructure {
+		if ib.ctx != nil {
+			if err := ib.ctx.Close(); err != nil {
+				errs = append(errs, err)
+			}
 		}
-	}
-	if ib.browser != nil {
-		if err := ib.browser.Close(); err != nil {
-			errs = append(errs, err)
+		if ib.browser != nil {
+			if err := ib.browser.Close(); err != nil {
+				errs = append(errs, err)
+			}
 		}
-	}
-	if ib.pw != nil {
-		if err := ib.pw.Stop(); err != nil {
-			errs = append(errs, err)
+		if ib.pw != nil {
+			if err := ib.pw.Stop(); err != nil {
+				errs = append(errs, err)
+			}
 		}
 	}
 	if len(errs) > 0 {