feat: add SetDefaultTimeout to InteractiveBrowser interface

Adds SetDefaultTimeout(time.Duration) to the InteractiveBrowser interface,
delegating to Playwright's Page and BrowserContext SetDefaultTimeout and
SetDefaultNavigationTimeout methods. This allows callers to set a timeout
so Playwright operations return an error instead of blocking forever when
the browser process crashes or the remote server becomes unresponsive.

Closes #86

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

promote_test.go

@@ -3,6 +3,7 @@ package extractor
 import (
 	"errors"
 	"testing"
+	"time"
 )
 
 // mockInteractiveBrowser implements InteractiveBrowser for testing without Playwright.
@@ -22,6 +23,7 @@ func (m mockInteractiveBrowser) KeyboardPress(string) error             { return
 func (m mockInteractiveBrowser) KeyboardInsertText(string) error        { return nil }
 func (m mockInteractiveBrowser) Screenshot(int) ([]byte, error)         { return nil, nil }
 func (m mockInteractiveBrowser) Cookies() ([]Cookie, error)             { return nil, nil }
+func (m mockInteractiveBrowser) SetDefaultTimeout(time.Duration)        {}
 func (m mockInteractiveBrowser) Close() error                           { return nil }
 
 func TestPromoteToInteractive_NonPromotable(t *testing.T) {