feat: adaptive quality in desktop, relay quality directive, Oboe state polling

- Wire AdaptiveQualityController into desktop engine send/recv tasks
  (mirrors Android pattern: AtomicU8 pending_profile, auto-mode check)
- Wire same into Android engine send task (was only in recv before)
- QualityDirective SignalMessage variant for relay-initiated codec switch
- ParticipantQuality tracking in relay RoomManager (per-participant
  AdaptiveQualityController, weakest-link tier computation)
- Relay broadcasts QualityDirective to all participants when room-wide
  tier degrades (coordinated codec switching)
- Oboe stream state polling: poll getState() for up to 2s after
  requestStart() to ensure both streams reach Started before proceeding
  (fixes intermittent silent calls on cold start, Nothing Phone A059)

Tasks: #7, #25, #26, #31, #35

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-client/src/featherchat.rs

@@ -131,6 +131,7 @@ pub fn signal_to_call_type(signal: &SignalMessage) -> CallSignalType {
         // bridge. Catch-all mapping for completeness.
         SignalMessage::FederatedSignalForward { .. } => CallSignalType::Offer,
         SignalMessage::MediaPathReport { .. } => CallSignalType::Offer, // control-plane
+        SignalMessage::QualityDirective { .. } => CallSignalType::Offer, // relay-initiated
     }
 }