refactor: upgrade to stagehand v3#15

Kylejeong2 wants to merge 1 commit intomainbrowserbase/agent-browse:mainfrom

kylejeong/stg-961-migrate-agent-browse-to-stagehand-v3browserbase/agent-browse:kylejeong/stg-961-migrate-agent-browse-to-stagehand-v3Copy head branch name to clipboard