API-level metadata

Static metadata about the v2 API. Supported symbol and exchange catalogs, the full error code list with HTTP status mapping, the auth scheme, the rate-limit ladder, the response envelope shape, and links to the OpenAPI spec / Swagger UI / ReDoc / endpoint catalog. Cheap (in-memory, no I/O).

Requires X-API-Key like every other v2 route — anonymous discovery is via /v2/openapi.json (FastAPI standard, no auth).