refactor(rest): move the discovery and OpenAPI registrar bodies into discovery-routes.ts

Move only. The bodies of RestServer#registerDiscoveryEndpoints and
RestServer#registerOpenApiEndpoints move, re-indented one level, to one new
module; the class keeps both private methods as a host literal plus .call.
routeManager goes by value, config as a getter. The one changed token is the
OpenAPI body's call of the private static overlayDocumentationInfo, now
reached through the host. The registrar list gains the module (7 -> 8).
Readers are re-pointed in the following commit.

Claude-Session: https://claude.ai/code/session_01Q9PZ5Pzqcus4woVvTZwWNU
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude