fix(notifications): handle FGS-not-allowed exception from background

AlwaysOnNotificationServiceManager calls NotificationRelayService.start()
from a flow collector that can fire during cold-start (before the activity
reaches foreground), where Android 12+ blocks startForegroundService() with
ForegroundServiceStartNotAllowedException. The exception was already caught
but logged as an error.

- Distinguish ForegroundServiceStartNotAllowedException from real failures
  and log it at WARN — the other layers (boot receiver, watchdog alarm,
  catch-up worker) retry from contexts that have FGS exemption.
- Retry the start in MainActivity.onResume() so the service comes up as
  soon as the user opens the app.

amethyst/src/main/java/com/vitorpamplona/amethyst/service/notifications/NotificationRelayService.kt

@@ -89,9 +89,22 @@ class NotificationRelayService : Service() {
             try {
                 ContextCompat.startForegroundService(context, intent)
             } catch (e: Exception) {
+                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S &&
+                    e is ForegroundServiceStartNotAllowedException
+                ) {
+                    // Android 12+ blocks startForegroundService() from the background unless
+                    // the caller has a temporary FGS exemption (e.g. broadcast receiver,
+                    // exact alarm, high-priority FCM). Cold-start triggered by a flow emission
+                    // from AlwaysOnNotificationServiceManager hits this path. The other
+                    // notification layers (BootCompletedReceiver, ServiceWatchdogManager,
+                    // NotificationCatchUpWorker) plus MainActivity.onResume retry from
+                    // contexts that are allowed.
+                    Log.w(TAG) { "Foreground service start not allowed from background; will retry from another layer" }
+                } else {
                     Log.e(TAG, "Failed to start foreground service", e)
                 }
             }
+        }
 
         fun stop(context: Context) {
             context.stopService(Intent(context, NotificationRelayService::class.java))

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/MainActivity.kt

@@ -31,6 +31,7 @@ import com.vitorpamplona.amethyst.debugState
 import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.model.LocalCache
 import com.vitorpamplona.amethyst.service.lang.LanguageTranslatorService
+import com.vitorpamplona.amethyst.service.notifications.NotificationRelayService
 import com.vitorpamplona.amethyst.service.playback.composable.DEFAULT_MUTED_SETTING
 import com.vitorpamplona.amethyst.service.playback.pip.BackgroundMedia
 import com.vitorpamplona.amethyst.ui.navigation.findParameterValue
@@ -89,6 +90,13 @@ class MainActivity : AppCompatActivity() {
 
         // starts muted every time
         DEFAULT_MUTED_SETTING.value = true
+
+        // If always-on notifications are enabled but the foreground service couldn't be
+        // started from the background during cold-start (Android 12+ restriction), retry
+        // now that the activity is in the foreground.
+        if (NotificationRelayService.isEnabled(this)) {
+            NotificationRelayService.start(this)
+        }
     }
 
     override fun onPause() {