feat: show usage pace icons on weekly and monthly bars

[shayan-ys]

What and why

A usage percentage alone does not say whether you are going too fast. 34% of a monthly quota is fine with 11 days left and bad with 25 days left. Weekly and monthly bars now show a pace icon beside the percentage.

7d               67% >        2d15h     a bit too fast
7d fable         58% |        2d15h     on pace
cursor mo     << 34%         11d01h     well under: quota to spare

Icon	Points from pace	Meaning
|	less than 5	On pace
> >> >>>	5, 15, 30 or more ahead	Too fast
< << <<<	5, 15, 30 or more behind	Too slow; quota to spare

• Points from pace is used% − time gone%. With 34% used and 63% of the month gone, you are 29 points behind: <<.
• Placement. Fast and on-pace icons sit one space right of the value; slow icons sit one space left of it. The value keeps its centred position, so a row does not shift when an icon appears. On the empty part of the bar, the icon has its own colour: yellow to red when too fast, blue when too slow. On the filled part, it uses the bar's dark text colour, because a red or orange icon on the amber-to-red fill would be hard to read. The icon's shape still carries the meaning there.
• Noise guard. No icon on windows shorter than 2 days (5h), in the first 10% of a window, in the first 12 hours, or on exhausted limits.
• Monthly windows. omp gives no durationMs for Cursor's monthly window, so its start is the same day one calendar month before the reset. If that day does not exist, it is the last day of that month: a reset on 31 March starts on 28 February.
• Config. usage.pace = false hides the icons.

Design notes

Before the icons, two other versions were tried:

• an inverted "time gone" cell in the bar, which read as a rendering glitch
• the icons in a separate column

The icons beside the value add no row or column.

Checklist

• uv run pytest (44 passed) and uv run ruff check . pass
• Tests cover the monthly start clamp, the pace points, every icon step, the hidden cases, icon placement, and the usage.pace = false path
• CHANGELOG.md has a line under Unreleased
• README image regenerated (uv run python scripts/screenshot.py)