Problem: with the project's Time Display Style set to Frames, the
current-time display showed frame numbers but the Timeline ruler kept
labelling its ticks in seconds:frames (`00:15f`). The label format was
hard-coded and never read the project settings.
Fix: a `ruler_label` helper prints the frame number in Frames mode the
same way the current-time display does (`{:05}`, counted from Start
Numbering Frames At), and keeps seconds:frames for the other styles.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
