Premium Analytics: Keep the first and last time-axis tick labels inside the chart

[chihsuan]

Fixes UNI-753.

Proposed changes

• Reserve half the width of the first and last x-axis tick labels in useChartMargin, so a label centred on the edge of the plot area no longer hangs outside the chart SVG.
• Measure those labels at the axis font size. The theme carries a unitless fontSize, which CSSOM drops, so they were otherwise measured at whatever the host body inherits.
• Drop the hardcoded right: 0 margin override from the Premium Analytics comparative line and bar charts, which is why the last date was clipped there.
• Skip the reservation when the x axis is hidden, and leave the compact sparkline branch on exactly the margins it had.

The y-axis half of useChartMargin already measures its widest label to size its gutter; the x-axis half only had a fixed 20px. Premium Analytics then overrode that to 0, on the reasoning that "the y-axis is on the left, so the right margin is always 0", which missed that the right margin is what the last x-axis label needs.

Related product discussion/links

• UNI-753

Does this pull request change what data or activity we track or use?

No.

Testing instructions

• Open the Premium Analytics dashboard on a site that has stats data, Traffic tab, Last 30 days.
• Look at the right-hand end of the Traffic summary chart's horizontal axis. The final date should be fully readable rather than sliced in half.
• Switch the chart to bars with the control in the widget header and check the same thing.
• Worth a look in a locale where September abbreviates to "Sept" (en-GB and most non-US English), which is where this was first noticed.

Before:

After:

[github-actions]

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/js-packages/charts/src/hooks/use-chart-margin.tsx	51/51 (100.00%)	0.00%	0 💚
projects/packages/premium-analytics/packages/widgets-toolkit/src/components/chart-comparative-bar/comparative-bar-chart.tsx	64/65 (98.46%)	-0.02%	0 💚
projects/packages/premium-analytics/packages/widgets-toolkit/src/components/chart-comparative-line/comparative-line-chart.tsx	38/52 (73.08%)	-0.51%	0 💚

1 file is newly checked for coverage.

File	Coverage
projects/js-packages/charts/src/utils/get-edge-tick-widths.ts	7/7 (100.00%) 💚

Full summary · PHP report · JS report