Agent Browser movies not very good

[jlewi]

Working with #139
It looks like the movies recorded in CI aren't great; often very short and miss key functionality.
codex says its partly due to running headless and the recording relying on browser action.

Would it be better to take screenshots explicitly and then turn them into a movie?

codex also mentioned.

BrowserManager.startScreencast(...)

[jlewi-openai]

Cleanup review: the CUJ runner now explicitly waits for movie files to exist and stabilize, uploads every .webm, and publishes inline preview/index links. Individual scenarios also add recording delays and movie checks. Those changes improve reliability, but there is still no quality/coverage assertion that a movie contains the key CUJ interactions rather than merely existing. Keeping open.