Copies a theme template into the site's per-theme overlay with a recorded provenance header (theme, version, content hash).
Never hand-copy a theme file: the header is what lets theme.diff
three-way-merge upgrades later instead of your copy silently freezing.
Usage
mix cherry.theme.eject TEMPLATE [--source DIR] [--force] [--json]
mix cherry.theme.eject --all [--source DIR] [--force] [--json]