feat: add real audio pipeline with Opus + RaptorQ FEC

- AudioPipeline: Kotlin AudioRecord/AudioTrack on JVM threads, PCM
  shuttled to Rust via lock-free ring buffers + JNI
- FEC: RaptorQ fountain codes on encode (5 frames/block, 20% repair
  ratio for GOOD profile), decoder feeds repair symbols for recovery
- Real audio level meter from mic RMS (replaces fake animation)
- Room name editable in UI (default: "android")
- Relay changed to pangolin.manko.yoga:4433
- Stats overlay shows FEC recovered count
- CallState now synced from polled stats (fixes "Connecting" stuck bug)

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

android/app/src/main/java/com/wzp/engine/WzpEngine.kt

@@ -97,6 +97,24 @@ class WzpEngine(private val callback: WzpCallback) {
         }
     }
 
+    /**
+     * Write captured PCM samples into the engine's capture ring buffer.
+     * Called from the AudioRecord capture thread.
+     */
+    fun writeAudio(pcm: ShortArray): Int {
+        if (nativeHandle == 0L) return 0
+        return nativeWriteAudio(nativeHandle, pcm)
+    }
+
+    /**
+     * Read decoded PCM samples from the engine's playout ring buffer.
+     * Called from the AudioTrack playout thread.
+     */
+    fun readAudio(pcm: ShortArray): Int {
+        if (nativeHandle == 0L) return 0
+        return nativeReadAudio(nativeHandle, pcm)
+    }
+
     // -- JNI native methods --------------------------------------------------
 
     private external fun nativeInit(): Long
@@ -108,6 +126,8 @@ class WzpEngine(private val callback: WzpCallback) {
     private external fun nativeSetSpeaker(handle: Long, speaker: Boolean)
     private external fun nativeGetStats(handle: Long): String?
     private external fun nativeForceProfile(handle: Long, profile: Int)
+    private external fun nativeWriteAudio(handle: Long, pcm: ShortArray): Int
+    private external fun nativeReadAudio(handle: Long, pcm: ShortArray): Int
     private external fun nativeDestroy(handle: Long)
 
     companion object {