feat: dark mode background fixes, chat bubble long-press menu, notification dedup, biometric auth for clear

- Fix: dark mode white backgrounds via transparent windowBackground, decorView color, and explicit Surface backgrounds on IoT/Profile/MainScreen
- Fix: dark mode text colors in ProfileScreen (nickname, account info, assistant status)
- Feat: long-press chat bubble to copy message text via DropdownMenu
- Feat: notification deduplication — track notified message IDs, clear on foreground
- Feat: cancel all notifications when app enters foreground
- Feat: biometric/device-credential verification before clearing local messages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/src/main/java/top/yeij/cyrene/CyreneApplication.kt

@@ -25,6 +25,8 @@ class CyreneApplication : Application() {
 
     private val initScope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
     private val activityCount = AtomicInteger(0)
+    @Volatile
+    private var notificationHelper: NotificationHelper? = null
 
     override fun onCreate() {
         super.onCreate()
@@ -40,6 +42,7 @@ class CyreneApplication : Application() {
             override fun onActivityStarted(activity: Activity) {
                 if (activityCount.incrementAndGet() == 1) {
                     RuntimeLog.general("app", "App in foreground")
+                    notificationHelper?.cancelAll()
                     getRepo()?.onAppForeground()
                 }
             }
@@ -60,10 +63,11 @@ class CyreneApplication : Application() {
 
         // Set up background notification callback once Koin is ready
         initScope.launch {
-            val notificationHelper = NotificationHelper(this@CyreneApplication)
+            val helper = NotificationHelper(this@CyreneApplication)
+            notificationHelper = helper
             val repo = getRepo()
             repo?.setNotificationCallback { message ->
-                notificationHelper.showMessageNotification(message)
+                helper.showMessageNotification(message)
             }
         }