feat: full quality tiers + slider UI + key-change warning on Android

1. Wire protocol: add Opus 32k/48k/64k (CodecId 6/7/8) + STUDIO
   profiles with is_opus() helper. Opus enc/dec accept all Opus variants.

2. JNI bridge: expand profile_from_int to 7 levels (0-6) mapping to
   GOOD, DEGRADED, CATASTROPHIC, Codec2_3200, STUDIO_32K/48K/64K.

3. Settings UI: replace radio buttons with Material3 Slider — 7 stops
   from Studio 64k (green) to Codec2 1.2k (dark red), matching desktop.

4. Key-change warning: AlertDialog on connect when server fingerprint
   has changed. Shows old vs new fingerprint, Accept New Key or Cancel.
   Accepting saves the new fingerprint and proceeds with the call.

5. Engine recv: handle studio codec IDs in auto-switch path.

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

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

@@ -109,10 +109,15 @@ class CallViewModel : ViewModel(), WzpCallback {
     private val _debugRecording = MutableStateFlow(false)
     val debugRecording: StateFlow<Boolean> = _debugRecording.asStateFlow()
 
-    // 0 = Opus (GOOD), 1 = Opus Low (DEGRADED), 2 = Codec2 (CATASTROPHIC)
+    // Quality profile index (matches JNI bridge profile_from_int)
     private val _codecChoice = MutableStateFlow(0)
     val codecChoice: StateFlow<Int> = _codecChoice.asStateFlow()
 
+    /** Key-change warning dialog state. */
+    data class KeyWarningInfo(val address: String, val oldFp: String, val newFp: String)
+    private val _keyWarning = MutableStateFlow<KeyWarningInfo?>(null)
+    val keyWarning: StateFlow<KeyWarningInfo?> = _keyWarning.asStateFlow()
+
     /** True when a call just ended and debug report can be sent. */
     private val _debugReportAvailable = MutableStateFlow(false)
     val debugReportAvailable: StateFlow<Boolean> = _debugReportAvailable.asStateFlow()
@@ -385,7 +390,35 @@ class CallViewModel : ViewModel(), WzpCallback {
         Log.i(TAG, "teardown: done")
     }
 
+    /** Accept the new server key and proceed with the call. */
+    fun acceptNewFingerprint() {
+        val info = _keyWarning.value ?: return
+        _knownFingerprints.value = _knownFingerprints.value.toMutableMap().also {
+            it[info.address] = info.newFp
+        }
+        settings?.saveServerFingerprint(info.address, info.newFp)
+        _keyWarning.value = null
+        startCallInternal()
+    }
+
+    fun dismissKeyWarning() {
+        _keyWarning.value = null
+    }
+
     fun startCall() {
+        val serverEntry = _servers.value[_selectedServer.value]
+        // Check for key change before connecting
+        val ls = lockStatus(serverEntry.address)
+        if (ls == LockStatus.CHANGED) {
+            val known = _knownFingerprints.value[serverEntry.address] ?: ""
+            val current = _pingResults.value[serverEntry.address]?.serverFingerprint ?: ""
+            _keyWarning.value = KeyWarningInfo(serverEntry.address, known, current)
+            return
+        }
+        startCallInternal()
+    }
+
+    private fun startCallInternal() {
         val serverEntry = _servers.value[_selectedServer.value]
         val room = _roomName.value
         Log.i(TAG, "startCall: server=${serverEntry.address} room=$room")

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

@@ -45,6 +45,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
@@ -89,6 +90,50 @@ fun InCallScreen(
     val pingResults by viewModel.pingResults.collectAsState()
 
     var showManageRelays by remember { mutableStateOf(false) }
+    val keyWarning by viewModel.keyWarning.collectAsState()
+
+    // Key-change warning dialog
+    keyWarning?.let { info ->
+        AlertDialog(
+            onDismissRequest = { viewModel.dismissKeyWarning() },
+            title = {
+                Column(horizontalAlignment = Alignment.CenterHorizontally, modifier = Modifier.fillMaxWidth()) {
+                    Text("\u26A0\uFE0F", fontSize = 40.sp)
+                    Spacer(modifier = Modifier.height(8.dp))
+                    Text("Server Key Changed", fontWeight = FontWeight.Bold)
+                }
+            },
+            text = {
+                Column {
+                    Text(
+                        "The relay's identity has changed since you last connected. " +
+                        "This usually happens when the server was restarted.",
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant
+                    )
+                    Spacer(modifier = Modifier.height(12.dp))
+                    Text("Previously known", style = MaterialTheme.typography.labelSmall, color = MaterialTheme.colorScheme.onSurfaceVariant)
+                    Text(info.oldFp, fontFamily = FontFamily.Monospace, style = MaterialTheme.typography.bodySmall)
+                    Spacer(modifier = Modifier.height(8.dp))
+                    Text("New key", style = MaterialTheme.typography.labelSmall, color = MaterialTheme.colorScheme.onSurfaceVariant)
+                    Text(info.newFp, fontFamily = FontFamily.Monospace, style = MaterialTheme.typography.bodySmall)
+                }
+            },
+            confirmButton = {
+                Button(
+                    onClick = { viewModel.acceptNewFingerprint() },
+                    colors = ButtonDefaults.buttonColors(containerColor = Color(0xFFFACC15))
+                ) {
+                    Text("Accept New Key", color = Color.Black, fontWeight = FontWeight.Bold)
+                }
+            },
+            dismissButton = {
+                TextButton(onClick = { viewModel.dismissKeyWarning() }) {
+                    Text("Cancel")
+                }
+            }
+        )
+    }
 
     // Ping once on launch, then every 5 minutes
     LaunchedEffect(Unit) {

android/app/src/main/java/com/wzp/ui/settings/SettingsScreen.kt

@@ -50,6 +50,9 @@ import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import com.wzp.ui.call.CallViewModel
 import com.wzp.ui.call.ServerEntry
@@ -245,31 +248,47 @@ fun SettingsScreen(
 
             Spacer(modifier = Modifier.height(12.dp))
 
-            // Codec selection
-            val codecNames = listOf("Opus 24k (Best)", "Opus 6k (Low BW)", "Codec2 1.2k (Minimal)")
+            // Quality selection — slider from best (studio 64k) to worst (codec2 1.2k)
+            val qualityLabels = listOf(
+                "Studio 64k", "Studio 48k", "Studio 32k", "Opus 24k",
+                "Opus 6k", "Codec2 1.2k", "Codec2 3.2k"
+            )
+            // Map slider position to JNI profile int:
+            // 0=Studio64k(6), 1=Studio48k(5), 2=Studio32k(4), 3=Opus24k(0),
+            // 4=Opus6k(1), 5=Codec2_1.2k(2), 6=Codec2_3.2k(3)
+            val sliderToProfile = intArrayOf(6, 5, 4, 0, 1, 2, 3)
+            val profileToSlider = mapOf(6 to 0, 5 to 1, 4 to 2, 0 to 3, 1 to 4, 2 to 5, 3 to 6)
+            val qualityColors = listOf(
+                Color(0xFF22C55E), Color(0xFF4ADE80), Color(0xFF86EFAC), Color(0xFFA3E635),
+                Color(0xFFFACC15), Color(0xFF991B1B), Color(0xFFE97320)
+            )
             val currentCodec by viewModel.codecChoice.collectAsState()
-            Text("Encode Codec", style = MaterialTheme.typography.bodyMedium)
+            val sliderPos = profileToSlider[currentCodec] ?: 3
+            Text("Quality", style = MaterialTheme.typography.bodyMedium)
             Text(
                 text = "Decode always accepts all codecs",
                 style = MaterialTheme.typography.bodySmall,
                 color = MaterialTheme.colorScheme.onSurfaceVariant
             )
             Spacer(modifier = Modifier.height(4.dp))
-            codecNames.forEachIndexed { idx, name ->
-                Row(
-                    verticalAlignment = Alignment.CenterVertically,
-                    modifier = Modifier
-                        .fillMaxWidth()
-                        .clickable { viewModel.setCodecChoice(idx) }
-                        .padding(vertical = 4.dp)
-                ) {
-                    RadioButton(
-                        selected = currentCodec == idx,
-                        onClick = { viewModel.setCodecChoice(idx) }
-                    )
-                    Spacer(modifier = Modifier.width(8.dp))
-                    Text(name, style = MaterialTheme.typography.bodyMedium)
-                }
+            Text(
+                text = qualityLabels[sliderPos],
+                style = MaterialTheme.typography.titleMedium.copy(fontWeight = FontWeight.Bold),
+                color = qualityColors[sliderPos]
+            )
+            Slider(
+                value = sliderPos.toFloat(),
+                onValueChange = { viewModel.setCodecChoice(sliderToProfile[it.toInt()]) },
+                valueRange = 0f..6f,
+                steps = 5,
+                modifier = Modifier.fillMaxWidth()
+            )
+            Row(
+                modifier = Modifier.fillMaxWidth(),
+                horizontalArrangement = Arrangement.SpaceBetween
+            ) {
+                Text("Best", style = MaterialTheme.typography.labelSmall, color = Color(0xFF22C55E))
+                Text("Lowest", style = MaterialTheme.typography.labelSmall, color = Color(0xFF991B1B))
             }
 
             Spacer(modifier = Modifier.height(24.dp))