Registry compatibility baselines

Each vN-validator.mjs is a frozen, standalone bundle of the Zod schemas understood by the first client for registry schema version N. CI validates every candidate catalog with the current version's baseline before it can be published to x-files/provider-registry/vN/.

The validator files are immutable. If a catalog no longer validates, either keep the wire data compatible or increment REGISTRY_SCHEMA_VERSION by one and create the next baseline:

pnpm --filter @cherrystudio/provider-registry compat:baseline

Never edit, regenerate, or delete an existing validator. A schema refactor that leaves the emitted catalog compatible does not require a version bump.