feat: wire QUIC transport, JNI bridge, connect UI + add docs

- Replace raw FFI with proper `jni` crate for string marshalling
- Wire QUIC transport in engine: connect to relay, crypto handshake
  (CallOffer/CallAnswer, X25519+Ed25519), send/recv MediaPackets
- Feed received packets into jitter buffer (was previously ignored)
- Add connect screen UI with CALL button (idle state) and in-call
  controls (mute, speaker, hang up, live stats)
- Hardcode relay 172.16.81.125:4433, room "android"
- Add comprehensive docs in docs/android/:
  architecture.md (8 mermaid diagrams), build-guide.md,
  debugging.md, maintenance.md, roadmap.md

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

android/app/src/main/AndroidManifest.xml

@@ -10,13 +10,13 @@
     <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
 
     <application
-        android:name=".WzpApplication"
+        android:name="com.wzp.WzpApplication"
         android:label="WZ Phone"
         android:supportsRtl="true"
         android:theme="@android:style/Theme.Material.Light.NoActionBar">
 
         <activity
-            android:name=".ui.call.CallActivity"
+            android:name="com.wzp.ui.call.CallActivity"
             android:exported="true"
             android:launchMode="singleTask">
             <intent-filter>
@@ -26,7 +26,7 @@
         </activity>
 
         <service
-            android:name=".service.CallService"
+            android:name="com.wzp.service.CallService"
             android:foregroundServiceType="phoneCall"
             android:exported="false" />
     </application>