feat: settings page with persistence, client alias in handshake, fix null fingerprints

- Add SettingsScreen with identity (alias, key backup/restore), audio defaults,
  server management, network prefs, and default room
- SettingsRepository persists all settings via SharedPreferences
- Auto-generate random display names on first launch (e.g. "Swift Wolf")
- Thread alias through CallOffer → relay handshake → RoomUpdate broadcast
- Derive caller fingerprint from identity key in relay handshake (fixes null
  fingerprints when --auth-url is not set)
- Persist identity seed for stable fingerprints across reconnects
- Add alias field to SignalMessage::CallOffer (serde default for backward compat)

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

android/app/src/main/java/com/wzp/ui/call/CallActivity.kt

@@ -15,8 +15,13 @@ import androidx.compose.material3.dynamicLightColorScheme
 import androidx.compose.material3.lightColorScheme
 import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.platform.LocalContext
 import androidx.core.content.ContextCompat
+import com.wzp.ui.settings.SettingsScreen
 
 /**
  * Main activity hosting the in-call Compose UI.
@@ -43,12 +48,19 @@ class CallActivity : ComponentActivity() {
 
         setContent {
             WzpTheme {
-                InCallScreen(
-                    viewModel = viewModel,
-                    onHangUp = {
-                        viewModel.stopCall()
-                    }
-                )
+                var showSettings by remember { mutableStateOf(false) }
+                if (showSettings) {
+                    SettingsScreen(
+                        viewModel = viewModel,
+                        onBack = { showSettings = false }
+                    )
+                } else {
+                    InCallScreen(
+                        viewModel = viewModel,
+                        onHangUp = { viewModel.stopCall() },
+                        onOpenSettings = { showSettings = true }
+                    )
+                }
             }
         }
 

android/app/src/main/java/com/wzp/ui/call/CallViewModel.kt

@@ -6,6 +6,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.wzp.audio.AudioPipeline
 import com.wzp.audio.AudioRouteManager
+import com.wzp.data.SettingsRepository
 import com.wzp.engine.CallStats
 import com.wzp.service.CallService
 import com.wzp.engine.WzpCallback
@@ -31,6 +32,7 @@ class CallViewModel : ViewModel(), WzpCallback {
     private var audioRouteManager: AudioRouteManager? = null
     private var audioStarted = false
     private var appContext: Context? = null
+    private var settings: SettingsRepository? = null
 
     private val _callState = MutableStateFlow(0)
     val callState: StateFlow<Int> get() = _callState.asStateFlow()
@@ -68,6 +70,12 @@ class CallViewModel : ViewModel(), WzpCallback {
     private val _captureGainDb = MutableStateFlow(0f)
     val captureGainDb: StateFlow<Float> = _captureGainDb.asStateFlow()
 
+    private val _alias = MutableStateFlow("")
+    val alias: StateFlow<String> = _alias.asStateFlow()
+
+    private val _seedHex = MutableStateFlow("")
+    val seedHex: StateFlow<String> = _seedHex.asStateFlow()
+
     private var statsJob: Job? = null
 
     companion object {
@@ -88,20 +96,43 @@ class CallViewModel : ViewModel(), WzpCallback {
         if (audioRouteManager == null) {
             audioRouteManager = AudioRouteManager(appCtx)
         }
+        if (settings == null) {
+            settings = SettingsRepository(appCtx)
+            loadSettings()
+        }
+    }
+
+    private fun loadSettings() {
+        val s = settings ?: return
+        s.loadServers()?.let { saved ->
+            if (saved.isNotEmpty()) _servers.value = saved
+        }
+        _selectedServer.value = s.loadSelectedServer().coerceIn(0, _servers.value.lastIndex)
+        _roomName.value = s.loadRoom()
+        _alias.value = s.getOrCreateAlias()
+        _preferIPv6.value = s.loadPreferIPv6()
+        _playoutGainDb.value = s.loadPlayoutGain()
+        _captureGainDb.value = s.loadCaptureGain()
+        _seedHex.value = s.getOrCreateSeedHex()
     }
 
     fun selectServer(index: Int) {
         if (index in _servers.value.indices) {
             _selectedServer.value = index
+            settings?.saveSelectedServer(index)
         }
     }
 
-    fun setPreferIPv6(prefer: Boolean) { _preferIPv6.value = prefer }
+    fun setPreferIPv6(prefer: Boolean) {
+        _preferIPv6.value = prefer
+        settings?.savePreferIPv6(prefer)
+    }
 
     fun addServer(hostPort: String, label: String) {
         val current = _servers.value.toMutableList()
         current.add(ServerEntry(hostPort, label))
         _servers.value = current
+        settings?.saveServers(current)
     }
 
     fun removeServer(index: Int) {
@@ -113,19 +144,36 @@ class CallViewModel : ViewModel(), WzpCallback {
             if (_selectedServer.value >= current.size) {
                 _selectedServer.value = 0
             }
+            settings?.saveServers(current)
+            settings?.saveSelectedServer(_selectedServer.value)
         }
     }
 
-    fun setRoomName(name: String) { _roomName.value = name }
+    fun setRoomName(name: String) {
+        _roomName.value = name
+        settings?.saveRoom(name)
+    }
 
     fun setPlayoutGainDb(db: Float) {
         _playoutGainDb.value = db
         audioPipeline?.playoutGainDb = db
+        settings?.savePlayoutGain(db)
     }
 
     fun setCaptureGainDb(db: Float) {
         _captureGainDb.value = db
         audioPipeline?.captureGainDb = db
+        settings?.saveCaptureGain(db)
+    }
+
+    fun setAlias(alias: String) {
+        _alias.value = alias
+        settings?.saveAlias(alias)
+    }
+
+    fun restoreSeed(hex: String) {
+        _seedHex.value = hex
+        settings?.saveSeedHex(hex)
     }
 
     /**
@@ -203,8 +251,10 @@ class CallViewModel : ViewModel(), WzpCallback {
             viewModelScope.launch(kotlinx.coroutines.Dispatchers.IO) {
                 try {
                     val relay = resolveToIp(serverEntry.address)
-                    Log.i(TAG, "startCall: resolved=$relay, calling engine.startCall")
-                    val result = engine?.startCall(relay, room) ?: -1
+                    val seed = _seedHex.value
+                    val name = _alias.value
+                    Log.i(TAG, "startCall: resolved=$relay, alias=$name, calling engine.startCall")
+                    val result = engine?.startCall(relay, room, seedHex = seed, alias = name) ?: -1
                     Log.i(TAG, "startCall: engine returned $result")
                     // Only wire up notification callback after engine is running
                     CallService.onStopFromNotification = { stopCall() }

android/app/src/main/java/com/wzp/ui/call/InCallScreen.kt

@@ -54,7 +54,8 @@ import kotlin.math.roundToInt
 @Composable
 fun InCallScreen(
     viewModel: CallViewModel,
-    onHangUp: () -> Unit
+    onHangUp: () -> Unit,
+    onOpenSettings: () -> Unit = {}
 ) {
     val callState by viewModel.callState.collectAsState()
     val isMuted by viewModel.isMuted.collectAsState()
@@ -82,7 +83,16 @@ fun InCallScreen(
                 .verticalScroll(rememberScrollState()),
             horizontalAlignment = Alignment.CenterHorizontally
         ) {
-            Spacer(modifier = Modifier.height(48.dp))
+            // Settings button (top-right)
+            if (callState == 0) {
+                Row(modifier = Modifier.fillMaxWidth(), horizontalArrangement = Arrangement.End) {
+                    TextButton(onClick = onOpenSettings) {
+                        Text("Settings")
+                    }
+                }
+            }
+
+            Spacer(modifier = Modifier.height(if (callState == 0) 16.dp else 48.dp))
 
             Text(
                 text = "WZ Phone",