feat(android): Bluetooth audio routing + network change detection + per-arch APK builds

Bluetooth: wire existing AudioRouteManager SCO support through both app
variants. Replace binary speaker toggle with 3-way route cycling
(Earpiece → Speaker → Bluetooth). Tauri side adds JNI bridge functions
(start/stop/query SCO, device availability) and Oboe stream restart.

Network awareness: integrate Android ConnectivityManager to detect
WiFi/cellular transitions and feed them to AdaptiveQualityController
via lock-free AtomicU8 signaling. Enables proactive quality downgrade
and FEC boost on network handoffs.

Build: add --arch flag to build-tauri-android.sh supporting arm64,
armv7, or all (separate per-arch APKs for smaller tester binaries).

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

crates/wzp-android/src/engine.rs

@@ -99,6 +99,9 @@ pub(crate) struct EngineState {
     /// QUIC transport handle — stored so stop_call() can close it immediately,
     /// triggering relay-side leave + RoomUpdate broadcast.
     pub quic_transport: Mutex<Option<Arc<wzp_transport::QuinnTransport>>>,
+    /// Network type from Android ConnectivityManager, polled by recv task.
+    /// 0xFF = no change pending; 0-5 = NetworkContext ordinal.
+    pub pending_network_type: AtomicU8,
 }
 
 pub struct WzpEngine {
@@ -120,6 +123,7 @@ impl WzpEngine {
             playout_ring: AudioRing::new(),
             audio_level_rms: AtomicU32::new(0),
             quic_transport: Mutex::new(None),
+            pending_network_type: AtomicU8::new(PROFILE_NO_CHANGE),
         });
         Self {
             state,
@@ -404,6 +408,13 @@ impl WzpEngine {
 
     pub fn force_profile(&self, _profile: QualityProfile) {}
 
+    /// Signal a network transport change from Android ConnectivityManager.
+    /// Stores the type atomically; the recv task polls it on each packet.
+    pub fn on_network_changed(&self, network_type: u8, bandwidth_kbps: u32) {
+        info!(network_type, bandwidth_kbps, "on_network_changed");
+        self.state.pending_network_type.store(network_type, Ordering::Release);
+    }
+
     pub fn get_stats(&self) -> CallStats {
         let mut stats = self.state.stats.lock().unwrap().clone();
         if let Some(start) = self.call_start {
@@ -871,6 +882,23 @@ async fn run_call(
                         );
                     }
 
+                    // Check for network transport change from ConnectivityManager
+                    {
+                        let net = state.pending_network_type.swap(PROFILE_NO_CHANGE, Ordering::Acquire);
+                        if net != PROFILE_NO_CHANGE {
+                            use wzp_proto::NetworkContext;
+                            let ctx = match net {
+                                0 => NetworkContext::WiFi,
+                                1 => NetworkContext::CellularLte,
+                                2 => NetworkContext::Cellular5g,
+                                3 => NetworkContext::Cellular3g,
+                                _ => NetworkContext::Unknown,
+                            };
+                            quality_ctrl.signal_network_change(ctx);
+                            info!(?ctx, "quality controller: network context updated");
+                        }
+                    }
+
                     // Adaptive quality: ingest quality reports from relay
                     if auto_profile {
                         if let Some(ref qr) = pkt.quality_report {

crates/wzp-android/src/jni_bridge.rs

@@ -222,6 +222,29 @@ pub unsafe extern "system" fn Java_com_wzp_engine_WzpEngine_nativeForceProfile(
     }));
 }
 
+/// Signal a network transport change from the Android ConnectivityManager.
+///
+/// `network_type` matches the Rust `NetworkContext` enum:
+///   0=WiFi, 1=CellularLte, 2=Cellular5g, 3=Cellular3g, 4=Unknown, 5=None
+///
+/// The engine forwards this to the `AdaptiveQualityController` which:
+/// - Preemptively downgrades one tier on WiFi→cellular
+/// - Activates a 10-second FEC boost
+/// - Uses faster downgrade thresholds on cellular
+#[unsafe(no_mangle)]
+pub unsafe extern "system" fn Java_com_wzp_engine_WzpEngine_nativeOnNetworkChanged(
+    _env: JNIEnv,
+    _class: JClass,
+    handle: jlong,
+    network_type: jint,
+    bandwidth_kbps: jint,
+) {
+    let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        let h = unsafe { handle_ref(handle) };
+        h.engine.on_network_changed(network_type as u8, bandwidth_kbps as u32);
+    }));
+}
+
 /// Write captured PCM samples from Kotlin AudioRecord into the engine's capture ring.
 /// pcm is a Java short[] array.
 #[unsafe(no_mangle)]