Stream the agent-to-business audio behind a playback token

Streams the saved audio as audio/mpeg. Mint the token with GET /voice/bridge/{id}/recording; this URL is what that endpoint returns as playback_url.

⛔ THERE IS NO Authorization HEADER ON THIS ENDPOINT, AND THAT IS DELIBERATE. A browser <audio src> cannot send one, so a byte endpoint that demanded a bearer token could not be played at all. The token in the path IS the credential: 256 random bits, checked against our database on every request including every seek, good for exactly one recording, and dead fifteen minutes after it was minted. Treat the whole URL as a secret with a short fuse, it is not an object-store link and there is nothing in it to decode.

RANGE REQUESTS ARE SUPPORTED AND ARE HOW SEEKING WORKS. Send Range: bytes=<start>-<end> and you get 206 with Content-Range; every response carries Accept-Ranges: bytes. A multi-range request, a non-bytes unit or a malformed header is IGNORED and answered 200 with the whole file rather than refused, so a player that asks badly still gets audio, it just does not get a seek.

⛔ EVERY REFUSAL IS THE SAME EMPTY 404: unknown token, expired token, revoked token, a recording that no longer belongs to the organization the token names, and a deployment with the feature off. Do not branch on the reason, because there is no reason in the response. If playback stops working, mint a new token; if that also fails, the audio is genuinely unavailable to you. A 502 is different and IS retryable: the token was good and the byte source failed.

SCOPE: agent-to-business audio only, exactly as on the mint endpoint. The Content-Disposition filename says so as well, because a downloaded file outlives the JSON that explained what it was. Responses are Cache-Control: private, no-store and Referrer-Policy: no-referrer; do not put them behind a shared cache.