Admin site graphs refer to wrong century

[abought]

Summary

Not urgent, but tracking the existence of this issue in case we start using these graphs for future reporting.

The admin site dashboard page shows a graph of jobs over time. In month view, the graph shows x axis labels referencing "1924".

The expected year label should be "2024".

A color legend might also be a nice usability enhancement. Right now, anyone we onboard has to either be told what the colors mean, or introspect the code to guess the meaning.