The app resolves light/dark from prefers-color-scheme and the user's
choice (body[data-ds-dark-theme]), but xterm and CodeMirror were pinned to
hardcoded dark themes — a light-mode user got a dark card inside a light
panel. New theme.ts reads the resolved scheme + token values and notifies
on flips (the presenter toggles the body attribute); the terminal now takes
its surface colors from the tokens and a curated one-dark/one-light ANSI
palette, and the editor gets a token-driven surface with the same curated
syntax palettes. Both re-theme in place on a scheme flip: the terminal
re-applies its theme, the editor reconfigures a Compartment holding only
the scheme-dependent extensions, so the document, undo history and scroll
survive. one-dark is dropped (superseded by the curated highlight style).