Month-over-month spend visualization (line / stacked bar chart)

The current spend-by-category pie chart shows a single time slice and is relative — there's no way to see how a category's spend changed in absolute terms month-over-month at a glance.

A line chart, stacked bar chart, or other comparative view would make it easy to spot outliers and unusual spend visually.

Even with the existing month browser (left/right buttons), comparison is broken by a loading spinner between months — the back-and-forth needed to compare isn't fluid.