storedPalette() reads and resolves the theme file without building the
engine, so onCreate can set the window background and system-bar icon
polarity before anything draws. Previously the background was a hex literal
in themes.xml and the bar icons were pinned dark, which meant every cold
start flashed one flavour's colour and Latte drew white icons on a
near-white page.
Adds the Material scheme mapping, type ramp and shape tokens the palette
feeds, plus unit tests for both.
nvrl