New: --recorder screencast captures via CDP with explicit per-frame timestamps. The assembled video starts exactly at the recording clock's zero — the calibration-flash mechanism (source of two past bugs) is skipped entirely for screencast renders, and frames arrive only when content changes. recordVideo remains the default; both live behind a new Recorder interface. Honest scope note: Chromium delivers screencast frames at CSS-viewport size regardless of deviceScaleFactor, so high-DPI capture (the issue's other goal) is not achievable this way — documented on #5. Closes #5.