A single Chart.js chart using axis stacking (scales.y.stack /
scales.y2.stack) renders two vertically stacked panels — price
on top, volume below. 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 volume
panel at the bottom, where navigation starts.