JustFrames does not log a wall-clock timestamp for recording start/stop

When building aind-data-schema Acquisition metadata, we need wall-clock start/end times for the behavior video DataStream. Currently the only wall-clock timestamp available is the date field in session_input.json, which reflects when the Bonsai session was launched — not when video recording actually began.

In my test recordings, Bonsai ran in editor mode for ~48 minutes before the video recording started. The session_input.json date is 14:09 PST but actual recording didn't start until ~14:58 PST (based on file modification times and co-recorded ephys data).

The metadata.csv ReferenceTime values and EndSession.json timestamp are Harp device clock seconds, which give accurate duration but can't be converted to wall-clock time without an external reference.

Request: Log a wall-clock timestamp (e.g., UTC datetime.now()) when Bonsai actually starts and stops writing video data — either as fields in session_output.json, as additional SoftwareEvent entries with both Harp and system timestamps, or similar.