Two new tests covering the user-acceptance criterion 'press → ptt
on, release → ptt off' through the full pipeline (backend press_gate
→ edge watcher → release tail → selector → real gate, identical to
what audioStats.pttActive reads in production):
* press_on_release_off_zero_tail — release_tail_ms = 0, transitions
are synchronous modulo one tokio tick.
* press_on_release_off_default_tail — release_tail_ms = 200,
transmit stays on briefly past key-up then transitions off.
cargo test --workspace --lib: 76 passed / 0 failed / 1 ignored.