feat(browser): complete camofox BrowserProvider with tabs, interaction, download capture and control lease
Contracts for browser API and browser.* agent capabilities; adapter implements
close/list/restore sessions, tabs + reconcile, history, click/type/select/scroll/press,
extract, waitForDownload (staged via DownloadSink, sha256), stale-ref guard and
automation/human actor check. testkit mock camofox gains an interactive site
(login redirect, captcha, click-driven page changes, downloads, PNG screenshots).
Co-Authored-By: Claude Opus 5.5 <[email protected]>