Status Chart: Fix mobile Safari

[StephanTLavavej]

My previous PR #2967 which attempted to address #2963 appeared to solve the problem for desktop Chrome, but broke mobile Safari such that the charts wouldn't even load.

I don't understand the root cause, but I suspect that it has something to do with how es-module-shims has to do actual work for mobile Safari (so perhaps the window is considered "loaded" before the JS finishes executing, and the addEventListener did nothing).

This PR uses a different technique that appears to work reliably in both environments. Now I run a function, check_css(), that detects whether Primer CSS has loaded. If it hasn't, we'll wait 50ms and check again. (Chosen semi-arbitrarily - we don't need to check every frame, but we do want to notice it quickly.)

This also updates dependencies slightly, including the Node version mentioned in the README.

As usual, this contains a "DROP BEFORE MERGING: Regen built/status_chart.mjs." commit to make the live preview work.

📉 📱 Live preview: stephantlavavej.github.io/STL/

[h-vetinari]

I didn't check the page between #2967 and this PR was merged, but now dark mode on firefox has no visible charts anymore (and refreshing doesn't help as it did pre-#2967).