Timeline Ruler: Fix main marker detection for sub-second intervals

Description

The main marker detection logic in the timeline ruler component may not work correctly for sub-second intervals (0.1s, 0.5s).

Problem

In apps/web/src/components/editor/timeline/timeline-ruler.tsx around lines 80-82, the current logic:

const isMainMarker = time % (interval >= 1 ? Math.max(1, interval) : 1) === 0;

When interval < 1, the expression Math.max(1, interval) always returns 1, making only time=0 a main marker. This could result in poor visual hierarchy for sub-second intervals where whole seconds should be emphasized as main markers.

Potential Fix

Consider changing the logic to:

const isMainMarker = interval >= 1 
  ? time % interval === 0
  : Math.abs(time % 1) < 0.0001; // Check if time is close to a whole second

Steps to Reproduce

1. Set timeline to high zoom level (triggers 0.1s or 0.5s intervals)
2. Observe timeline ruler markers
3. Check if whole seconds are properly emphasized as main markers

Reference

• PR: https://github.com/OpenCut-app/OpenCut/pull/324
• Comment: https://github.com/OpenCut-app/OpenCut/pull/324#discussion_r2211935409
• Reported by: @coderabbitai[bot]
• Requested by: @simonorzel26

Priority

Low - Visual enhancement that can be addressed in a separate cleanup PR.

Start in apps/web/src/components/editor/timeline/timeline-ruler.tsx around lines 80-82 and review the main-marker calculation. Reproduce the ruler at high zoom with 0.1s or 0.5s intervals, then verify that whole-second markers are emphasized while sub-second markers retain their normal hierarchy.