docs: say what the connection reads from the voice credential

It reads the token, model, transcription model and tier for diagnostics and
cost accounting, so the credential is not opaque to it. Also lists requestToken's
authMode option in APPLICATION.md.

docs/APPLICATION.md

@@ -158,7 +158,7 @@ routing and regional caches. Request parameters cannot override these endpoints.
 Voice controls accept an action runner and a controller factory through
 `createVoiceCommands` (`./voice/commands`). The default Realtime controller owns
 microphone tracks, playback, push-to-talk, tool cancellation and radio handoff.
-Its backend supplies `requestToken({ tier, signal })` and
+Its backend supplies `requestToken({ tier, authMode, signal })` and
 `negotiate({ offerSdp, credential, signal })`. The Realtime-compatible adapter
 (`./voice/realtime-backend`) accepts separate token and connection transports
 and endpoints. Only the short-lived client secret reaches the SDP endpoint.