mosadd-mtalk

Push-to-talk voice rooms on mosadd. Half-duplex floor control — one speaker at a time, FIFO queue, anti-hog auto-release. Use when the user wants a walkie-talkie style room, "open a PTT channel", join an ops/field-team room, or hold the floor to speak. NOT for full-duplex 1:1 voice (that's mDM_call_start).