docs/architecture/sdd.md: three new rows in the Audio Detailed Design table. 'VoiceActivity gate (capture-side)' documents voice_activity::VoiceActivityStateMachine — the 10 ms-cadence gate for TransmitMode::VoiceActivity with open-after (40 ms) / hangover (500 ms) / min-tx (200 ms) / weak-hold (30-100 frames) timers, plus live configure() re-clamping behaviour. 'macOS render cadence (producer + ring)' documents the 20 ms tokio producer task + crossbeam ArrayQueue ring with 100 ms prebuffer, the design chosen to decouple ingress quantums (20 ms Opus frames) from egress quantums (whatever VPIO asks for). 'iOS render cadence (direct-fill)' documents the direct-fill callback path with preallocated 4096x2 f32 scratch buffer and try_lock semantics (not blocking lock).
Closes the VoiceActivity / macOS-producer-ring / iOS-direct-fill doc gaps flagged in the PR #27 'Deferred' list.
Edison Jwa
581353b6d2