A thin primary-coloured indicator (leading dot + line) marks the current
time across today's column in the day and week timelines, positioned on the
same HOUR_HEIGHT scale as the event blocks so it lines up with the grid.
Shared ui/common/NowLine.kt ticks once a minute, re-aligning to each minute
boundary to avoid drift, and only mounts on today's column so a single
coroutine runs. Renders nothing when today isn't in view.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
