Return the built-in payload and linker reference catalogues.
The catalogue is static server-side reference data — no DB reads,
no org scoping. The endpoint still requires a bearer token so every
/v1 operation satisfies test_every_v1_operation_has_bearer_security
in the OpenAPI regression suite.
Cost: read — rate bucket only.
Bearer authentication header of the form Bearer <token>, where <token> is your auth token.