OpenCADStudio/plugins#901
- Record the host's rustc --version output in the embedded version_info.json.
- Add rustc_version/rustc_declared/rustc_compatible to plugin manifests and
release metadata, mirroring the existing acadrust gate.
- Reject API v4+ plugins whose declared rustc differs from the host, with a
clear one-line error message.
- Propagate the rustc gate through the marketplace, install flow, and UI.
- Update plugin architecture docs to describe the new ABI metadata.
Sebastian