A single Chart.js chart using axis stacking (scales.y.stack /
scales.y2.stack) renders two vertically stacked panels — volume
on top, price below: Chart.js stacks the scale declared last
(y2) at the top. MAIDR exposes each panel as its own subplot:
use arrow keys to move between subplots (Up Arrow moves to the panel
above), press 'Enter' to drill into a panel, and 'Escape' to return to
subplot navigation. Panels are numbered bottom-up — "Subplot 1" is the
price panel at the bottom, where navigation starts.