OptionalinitialOverride the default theme payload. If omitted, the service starts with
the canonical defaults (#0a0a0a / #e0e0e0 / #7aa2f7).
OptionalonCalled synchronously from publishTheme(theme) with a theme.changed
envelope. Intended for the shell adapter (Plan 13-02) to fan-out the
push to every registered napplet via the runtime's sendToNapplet
primitive.
Keep this callback shape framework-agnostic — the service does NOT import any shell / browser APIs.
Configuration for
createThemeService.Example