Implement services/list and services/schema in registry/discovery.rs: spec
constructors, factory handlers taking Arc<OperationRegistry>, JSON serialization
of OperationSpec (incl. error_schemas per ADR-023), leading-slash normalization
for services/schema, NOT_FOUND for unknown ops, INVALID_INPUT for missing name.
Both registered as Local provenance with empty authority/env/caps and empty
AccessControl.
Refs: docs/architecture/crates/call/operation-registry.md
Implements: ADR-023