feat: identicons, tap-to-copy fingerprint, recent rooms (Phase 1 backport)

Backport from desktop client to Android:

Identicons:
- New Identicon.kt composable: deterministic 5x5 symmetric Canvas pattern
  from fingerprint hash (same algorithm as desktop identicon.ts)
- Participant list shows identicon + name + tappable fingerprint
- Settings page shows identicon next to fingerprint

CopyableFingerprint:
- Tap any fingerprint text to copy to clipboard with Toast feedback
- Used in participant list and settings page

Recent rooms:
- SettingsRepository: persists last 5 (relay, room) pairs
- CallViewModel: saves on startCall, exposes as StateFlow
- InCallScreen: clickable chips that fill room + select matching server

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

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

@@ -70,6 +70,9 @@ class CallViewModel : ViewModel(), WzpCallback {
     private val _preferIPv6 = MutableStateFlow(false)
     val preferIPv6: StateFlow<Boolean> = _preferIPv6.asStateFlow()
 
+    private val _recentRooms = MutableStateFlow<List<com.wzp.data.SettingsRepository.RecentRoom>>(emptyList())
+    val recentRooms: StateFlow<List<com.wzp.data.SettingsRepository.RecentRoom>> = _recentRooms.asStateFlow()
+
     private val _playoutGainDb = MutableStateFlow(0f)
     val playoutGainDb: StateFlow<Float> = _playoutGainDb.asStateFlow()
 
@@ -139,6 +142,7 @@ class CallViewModel : ViewModel(), WzpCallback {
         _captureGainDb.value = s.loadCaptureGain()
         _seedHex.value = s.getOrCreateSeedHex()
         _aecEnabled.value = s.loadAecEnabled()
+        _recentRooms.value = s.loadRecentRooms()
     }
 
     fun selectServer(index: Int) {
@@ -287,6 +291,8 @@ class CallViewModel : ViewModel(), WzpCallback {
         _debugReportAvailable.value = false
         _debugReportStatus.value = null
         lastCallServer = serverEntry.address
+        settings?.addRecentRoom(serverEntry.address, room)
+        _recentRooms.value = settings?.loadRecentRooms() ?: emptyList()
         debugReporter?.prepareForCall()
         try {
             // Teardown previous call but don't stop the service (we're about to restart it)

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

@@ -42,6 +42,7 @@ import androidx.compose.ui.Alignment
 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.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
@@ -200,6 +201,36 @@ fun InCallScreen(
                     modifier = Modifier.fillMaxWidth(0.6f)
                 )
 
+                // Recent rooms
+                val recentRooms by viewModel.recentRooms.collectAsState()
+                if (recentRooms.isNotEmpty()) {
+                    Spacer(modifier = Modifier.height(8.dp))
+                    FlowRow(
+                        modifier = Modifier.fillMaxWidth(),
+                        horizontalArrangement = Arrangement.Center
+                    ) {
+                        recentRooms.forEach { recent ->
+                            Surface(
+                                onClick = {
+                                    viewModel.setRoomName(recent.room)
+                                    // Select matching server
+                                    val idx = servers.indexOfFirst { it.address == recent.relay }
+                                    if (idx >= 0) viewModel.selectServer(idx)
+                                },
+                                shape = RoundedCornerShape(16.dp),
+                                color = MaterialTheme.colorScheme.surfaceVariant,
+                                modifier = Modifier.padding(2.dp)
+                            ) {
+                                Text(
+                                    text = recent.room,
+                                    style = MaterialTheme.typography.labelSmall,
+                                    modifier = Modifier.padding(horizontal = 12.dp, vertical = 4.dp)
+                                )
+                            }
+                        }
+                    }
+                }
+
                 Spacer(modifier = Modifier.height(24.dp))
 
                 Button(
@@ -262,11 +293,33 @@ fun InCallScreen(
                         color = MaterialTheme.colorScheme.onSurfaceVariant
                     )
                     unique.forEach { member ->
-                        Text(
-                            text = member.displayName,
-                            style = MaterialTheme.typography.labelSmall,
-                            color = MaterialTheme.colorScheme.onSurfaceVariant
-                        )
+                        Row(
+                            verticalAlignment = Alignment.CenterVertically,
+                            modifier = Modifier.padding(vertical = 2.dp)
+                        ) {
+                            com.wzp.ui.components.Identicon(
+                                fingerprint = member.fingerprint.ifEmpty { member.displayName },
+                                size = 28.dp,
+                            )
+                            Spacer(modifier = Modifier.width(8.dp))
+                            Column {
+                                Text(
+                                    text = member.displayName,
+                                    style = MaterialTheme.typography.labelSmall,
+                                    color = MaterialTheme.colorScheme.onSurfaceVariant
+                                )
+                                if (member.fingerprint.isNotEmpty()) {
+                                    com.wzp.ui.components.CopyableFingerprint(
+                                        fingerprint = member.fingerprint.take(16),
+                                        style = MaterialTheme.typography.labelSmall.copy(
+                                            fontSize = 9.sp,
+                                            fontFamily = FontFamily.Monospace,
+                                        ),
+                                        color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.6f),
+                                    )
+                                }
+                            }
+                        }
                     }
                 }