//! Schema registry — placeholder for the future Rust analogue of
//! Pixar's `UsdSchemaRegistry`.
//!
//! The C++ registry maps schema type tokens (e.g. `"Mesh"`,
//! `"PhysicsRigidBodyAPI"`) to schema definitions: their fallback
//! property values, allowed token sets, applied-API flags, and
//! aliases. Once openusd-rs gains enough domain schemas to make a
//! shared lookup useful, this is where that registry will live.
//!
//! Today the per-schema readers in `super::physics` and `super::skel`
//! keep their own token constants and validation logic in-module —
//! the registry layer doesn't need to exist yet, and would just be
//! empty plumbing. The module exists as a clear signpost so future
//! contributions know where to grow.