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>

docs/PRD-bluetooth-audio.md

@@ -0,0 +1,98 @@
+# PRD: Bluetooth Audio Routing
+
+> Phase: Implemented  
+> Status: Ready for testing  
+> Platforms: Android (native Kotlin app + Tauri desktop app)
+
+## Problem
+
+WarzonePhone had `AudioRouteManager.kt` with complete Bluetooth SCO support, but it was disconnected from both UIs. Users with Bluetooth headsets had no way to route call audio to them.
+
+## Solution
+
+Wire Bluetooth SCO routing end-to-end through both app variants, replacing the binary speaker toggle with a 3-way audio route cycle: **Earpiece → Speaker → Bluetooth**.
+
+## Architecture
+
+```
+┌─────────────────────────────────────────────────────┐
+│ Native Kotlin App (com.wzp)                         │
+│                                                     │
+│  InCallScreen ──► CallViewModel ──► AudioRouteManager
+│  (Compose UI)     cycleAudioRoute()  setSpeaker()   │
+│  "Ear/Spk/BT"    audioRoute Flow     setBluetoothSco()
+│                                      isBluetoothAvailable()
+└─────────────────────────────────────────────────────┘
+
+┌─────────────────────────────────────────────────────┐
+│ Tauri Desktop App (com.wzp.desktop)                 │
+│                                                     │
+│  main.ts ──► Tauri Commands ──► android_audio.rs    │
+│  cycleAudioRoute()  set_bluetooth_sco()  JNI calls  │
+│  "Ear/Spk/BT"      is_bluetooth_available()         │
+│                     get_audio_route()                │
+│                                                     │
+│  After each route change: Oboe stop + start         │
+│  (spawn_blocking to avoid stalling tokio)           │
+└─────────────────────────────────────────────────────┘
+```
+
+## Components Modified
+
+### Native Kotlin App
+
+| File | Change |
+|------|--------|
+| `CallViewModel.kt` | Added `audioRoute: StateFlow<AudioRoute>`, `cycleAudioRoute()`, wired `onRouteChanged` callback |
+| `InCallScreen.kt` | `ControlRow` now takes `audioRoute: AudioRoute` + `onCycleRoute`, displays Ear/Spk/BT with distinct colors |
+
+### Tauri App
+
+| File | Change |
+|------|--------|
+| `android_audio.rs` | Added `start_bluetooth_sco()`, `stop_bluetooth_sco()`, `is_bluetooth_sco_on()`, `is_bluetooth_available()` |
+| `lib.rs` | Added `set_bluetooth_sco`, `is_bluetooth_available`, `get_audio_route` Tauri commands |
+| `main.ts` | Replaced `speakerphoneOn` toggle with `currentAudioRoute` cycling logic |
+| `style.css` | Added `.bt-on` CSS class (blue-400 highlight) |
+
+## Audio Route Lifecycle
+
+1. **Call starts** → route defaults to Earpiece
+2. **User taps route button** → cycles to next available route
+3. **Route changes** → AudioManager JNI call + Oboe stream restart (~60-400ms)
+4. **BT device disconnects mid-call** → `AudioDeviceCallback.onAudioDevicesRemoved` fires → auto-fallback to Earpiece/Speaker
+5. **Call ends** → route reset to Earpiece, BT SCO stopped
+
+## Route Cycling Logic
+
+```
+Available routes = [Earpiece, Speaker] + [Bluetooth] if SCO device connected
+
+Tap cycle:
+  Earpiece → Speaker → Bluetooth (if available) → Earpiece → ...
+
+If BT not available:
+  Earpiece → Speaker → Earpiece → ...
+```
+
+## Permissions
+
+- `BLUETOOTH_CONNECT` (Android 12+) — already in `AndroidManifest.xml`
+- `MODIFY_AUDIO_SETTINGS` — already in manifest
+
+## Known Limitations
+
+- **SCO only** — no A2DP (stereo music profile). SCO is correct for VoIP (bidirectional mono).
+- **Deprecated APIs** — `startBluetoothSco()`, `isBluetoothScoOn` are deprecated in API 31+ but still functional. Modern replacement `setCommunicationDevice()` requires API 31 and more complex device enumeration. Since minSdk is 26, deprecated path is correct.
+- **No auto-switch on BT connect** — when a BT device connects mid-call, `onRouteChanged` fires but we don't auto-switch. User must tap the button.
+
+## Testing
+
+1. Pair a Bluetooth SCO headset with Android device
+2. Start call → verify Earpiece is default
+3. Tap route → Speaker (audio moves to loudspeaker, button shows "Spk")
+4. Tap route → BT (audio moves to headset, button shows "BT", blue highlight)
+5. Tap route → Earpiece (audio back to earpiece, button shows "Ear")
+6. Disconnect BT mid-call → verify auto-fallback
+7. Verify both app variants work identically
+8. Verify no audio glitches during route transitions