New single-page app: two rendezvoused partners type the same code and get a
live Opus voice call over WebRTC — direct P2P when possible, TURN relay
fallback otherwise, DTLS-SRTP encrypted end to end. Reuses the zebra-signal
rendezvous (code-encrypted SDP, zero-knowledge relay) and the ephemeral
/turn-cred credentials. Mic uses echo-cancellation/noise-suppression; mute,
hang up, live mic/remote level meters, and a direct-vs-relayed path indicator.
Deliberately NOT over the volume modem — ordinary low-latency voice, which
doubles as a plausible cover for the report channel.