Handshake — version and discovery

Returns the implementing module's version, the handler name (always Stratos), and a link back to this documentation.

Used by the Stratos airline admin area to verify a newly-entered VA API base URL is reachable and speaking the Stratos contract — if the response shape matches and handler is Stratos, the setup is good.

{
  "api_version": "0.2.3",
  "handler": "Stratos"
}