fix(android): crash on back-while-streaming (UAF) + Material You theme & connect polish

Crash: DisposableEffect.onDispose called nativeClose(handle) (Box::from_raw frees
the SessionHandle) while the SurfaceView's surfaceDestroyed independently called
nativeStopVideo/Audio/Mic on the same handle -- whichever ran after the close
dereferenced freed memory (SIGSEGV: the consistent back-navigation crash). Add a
one-shot `closed` guard: onDispose marks it before freeing; surfaceDestroyed skips
the native calls once closed (backgrounding still stops the threads when it wins).

Polish:
- Branded Material You theme (Theme.kt): dynamic colour on Android 12+, punktfunk
  brand violets as the pre-12 fallback, replacing the generic darkColorScheme().
- ConnectScreen: "Connecting..." was rendered in error-red with no spinner; now a
  neutral spinner while connecting, red reserved for actual errors.

Verified locally: ./gradlew :app:assembleDebug BUILD SUCCESSFUL (both ABIs + the
Compose changes), debug APK assembles.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/android/app/src/main/kotlin/io/unom/punktfunk/ConnectScreen.kt

@@ -21,6 +21,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.lazy.grid.GridCells
 import androidx.compose.foundation.lazy.grid.GridItemSpan
 import androidx.compose.foundation.lazy.grid.LazyVerticalGrid
@@ -32,6 +33,7 @@ import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.Add
 import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.Button
+import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.ExtendedFloatingActionButton
 import androidx.compose.material3.Icon
@@ -207,12 +209,32 @@ fun ConnectScreen(settings: Settings, onConnected: (Long) -> Unit) {
                     Spacer(Modifier.height(24.dp))
 
                     status?.let {
+                        // While connecting it's progress (spinner, neutral); otherwise it's a
+                        // result/error (red). Previously every status showed in error-red, so a
+                        // normal "Connecting…" looked like a failure.
+                        if (connecting) {
+                            Row(
+                                verticalAlignment = Alignment.CenterVertically,
+                                horizontalArrangement = Arrangement.spacedBy(8.dp),
+                            ) {
+                                CircularProgressIndicator(
+                                    modifier = Modifier.size(16.dp),
+                                    strokeWidth = 2.dp,
+                                )
+                                Text(
+                                    it,
+                                    style = MaterialTheme.typography.bodyMedium,
+                                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                                )
+                            }
+                        } else {
                             Text(
                                 it,
                                 style = MaterialTheme.typography.bodySmall,
                                 color = MaterialTheme.colorScheme.error,
                                 textAlign = TextAlign.Center,
                             )
+                        }
                         Spacer(Modifier.height(16.dp))
                     }
                 }

clients/android/app/src/main/kotlin/io/unom/punktfunk/MainActivity.kt

@@ -9,9 +9,7 @@ import androidx.activity.SystemBarStyle
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
 import androidx.compose.foundation.layout.fillMaxSize
-import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
-import androidx.compose.material3.darkColorScheme
 import androidx.compose.ui.Modifier
 import io.unom.punktfunk.kit.Gamepad
 import io.unom.punktfunk.kit.Keymap
@@ -38,7 +36,7 @@ class MainActivity : ComponentActivity() {
             navigationBarStyle = SystemBarStyle.dark(android.graphics.Color.TRANSPARENT),
         )
         setContent {
-            MaterialTheme(colorScheme = darkColorScheme()) {
+            PunktfunkTheme {
                 Surface(modifier = Modifier.fillMaxSize()) { App() }
             }
         }

clients/android/app/src/main/kotlin/io/unom/punktfunk/StreamScreen.kt

@@ -39,6 +39,7 @@ import androidx.core.view.WindowInsetsControllerCompat
 import io.unom.punktfunk.kit.Gamepad
 import io.unom.punktfunk.kit.GamepadFeedback
 import io.unom.punktfunk.kit.NativeBridge
+import java.util.concurrent.atomic.AtomicBoolean
 import kotlinx.coroutines.delay
 import kotlin.math.abs
 import kotlin.math.roundToInt
@@ -70,6 +71,12 @@ fun StreamScreen(handle: Long, micEnabled: Boolean, onDisconnect: () -> Unit) {
         }
     }
 
+    // One-shot teardown guard. Both the SurfaceView callback and DisposableEffect tear down on the
+    // way out, but `nativeClose` frees the handle — so once it's closed, NO path may touch the handle
+    // again (use-after-free → SIGSEGV: the consistent back-while-streaming crash). Both run on the
+    // main thread, so a plain flag is race-free; AtomicBoolean just makes the intent explicit.
+    val closed = remember { AtomicBoolean(false) }
+
     DisposableEffect(handle) {
         window?.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
         controller?.let {
@@ -81,6 +88,7 @@ fun StreamScreen(handle: Long, micEnabled: Boolean, onDisconnect: () -> Unit) {
         // Host→client feedback (rumble + DualSense lightbar/LEDs); poll threads stopped before close.
         val feedback = GamepadFeedback(handle).also { it.start() }
         onDispose {
+            closed.set(true) // from here the handle gets freed; surfaceDestroyed must not touch it
             feedback.stop() // stop + join the poll threads BEFORE nativeClose frees the handle
             activity?.axisMapper?.reset() // release-all so nothing sticks on the host
             activity?.axisMapper = null
@@ -112,10 +120,16 @@ fun StreamScreen(handle: Long, micEnabled: Boolean, onDisconnect: () -> Unit) {
                         override fun surfaceChanged(holder: SurfaceHolder, format: Int, width: Int, height: Int) {}
 
                         override fun surfaceDestroyed(holder: SurfaceHolder) {
+                            // Surface gone (backgrounding, or on the way out). Stop the threads that
+                            // render to it — but only while the session is still open. Once
+                            // DisposableEffect has closed it, the handle is freed; dereferencing it
+                            // here is the use-after-free that crashed on back-navigation.
+                            if (!closed.get()) {
                                 NativeBridge.nativeStopMic(handle)
                                 NativeBridge.nativeStopAudio(handle)
                                 NativeBridge.nativeStopVideo(handle)
                             }
+                        }
                     })
                 }
             },

clients/android/app/src/main/kotlin/io/unom/punktfunk/Theme.kt

@@ -0,0 +1,43 @@
+package io.unom.punktfunk
+
+import android.os.Build
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.material3.dynamicDarkColorScheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+
+// punktfunk brand violets (from the app icon: #6C5BF3 / #A79FF8 / #D2C9FB on a #16132A indigo).
+// Used as the fallback dark scheme on pre-Android-12 devices; on 12+ we defer to Material You.
+private val BrandDark = darkColorScheme(
+    primary = Color(0xFFA79FF8),
+    onPrimary = Color(0xFF1B1442),
+    primaryContainer = Color(0xFF4C3FB3),
+    onPrimaryContainer = Color(0xFFE5E0FF),
+    secondary = Color(0xFFC8C2EC),
+    onSecondary = Color(0xFF2E2A4D),
+    tertiary = Color(0xFF8FD0E8),
+    onTertiary = Color(0xFF053543),
+    background = Color(0xFF131129),
+    onBackground = Color(0xFFE5E1F2),
+    surface = Color(0xFF1A1733),
+    onSurface = Color(0xFFE5E1F2),
+    surfaceVariant = Color(0xFF2A2647),
+    onSurfaceVariant = Color(0xFFC7C2DE),
+)
+
+/**
+ * App theme — always dark (a streaming client reads best on a dark canvas, and the immersive
+ * stream view assumes it), but uses **Material You** dynamic colour on Android 12+ so the UI
+ * harmonises with the user's wallpaper, falling back to the punktfunk brand violets below that.
+ */
+@Composable
+fun PunktfunkTheme(content: @Composable () -> Unit) {
+    val scheme = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+        dynamicDarkColorScheme(LocalContext.current)
+    } else {
+        BrandDark
+    }
+    MaterialTheme(colorScheme = scheme, content = content)
+}