Move the bgm vite plugin into the package so it can be tested in
isolation from the web app. Serve each package as a JSON module,
serializing its maps, and verify resolution through a real vite build
against a self-contained fixture.
Parse yaml/json/toml and markdown code blocks into packages, expanding
$variants via typed-csv and collecting parts, surfaces, and setups by
include patterns. Ships zod validation, a vitest config, and 16 tests.