The pinnable versions came only from db/data/framework_versions.yml, so
every design system release needed a trmnlp release before a plugin could
pin it. The design system now publishes that file in a public repo, so
read it there once per run and keep the bundled copy as the fallback when
the request fails or the response is not a version list.
Also refreshes the bundled copy: latest moves from 3.1.1 to 3.2.0.
Necessary to let a plugin pin the TRMNL Design System version it
renders against, rather than always tracking the latest release. The
framework_version setting round-trips through push and pull so the
choice stays in sync with the hosted plugin service, and the preview
exposes a picker for switching versions locally.