Invoke an externally-exposed swarm script

Runs the script bound to this endpoint and returns a JSON envelope { ok, result, error, durationMs } (HTTP 200) once execution is reached. Auth/routing failures use 401 (bad/missing bearer) and 404 (unknown or disabled endpoint). Optional X-Swarm-Timeout-Ms header (default 60000, clamped 1000–300000) sets the wall-clock timeout.