Get Active Streams

Get information about active audio streams (from Redis) and the Deepgram connection tracker (registered slots vs cap — includes any leaked slots, so tracker.active >> local_sessions means the slot leak is accumulating).

Admin only (2026-09-18 route-auth review). Session ids here are deepgram_{callId}_{userId}_{lang}_{ts}, so this list names who is in which room, alongside the per-session billable seconds; test_every_route_answers.py had it in its "worth a look" list as "ops telemetry with no auth". The loadtest and monitoring scripts under e2e/loadtest that read it now need an admin token.