Rename the plugin's virtual modules to virtual:bgm/packages and
virtual:bgm/package/<id> so they read as plugin-provided modules rather
than real packages. Update the unit and build integration tests.
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.