fix: add event dedup, back button handling, and wake lock for calls

- Deduplicate signaling events via processedEventIds set in
  CallManager to prevent duplicate processing from multiple relays
- BackHandler on CallScreen calls hangup() before navigating back
- KeepScreenOn composable adds FLAG_KEEP_SCREEN_ON during calls
  and clears it on dispose

https://claude.ai/code/session_017hZm7yu7CzmcQgZGSaqSXS

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/call/CallScreen.kt

@@ -20,6 +20,8 @@
  */
 package com.vitorpamplona.amethyst.ui.call
 
+import android.view.WindowManager
+import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
@@ -40,6 +42,7 @@ import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
@@ -50,6 +53,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
@@ -73,7 +77,13 @@ fun CallScreen(
 ) {
     val callState by callManager.state.collectAsState()
     val scope = rememberCoroutineScope()
-    val context = androidx.compose.ui.platform.LocalContext.current
+    val context = LocalContext.current
+
+    BackHandler(enabled = callState !is CallState.Idle && callState !is CallState.Ended) {
+        scope.launch { callManager.hangup() }
+    }
+
+    KeepScreenOn()
 
     when (val state = callState) {
         is CallState.Idle -> {
@@ -363,3 +373,15 @@ private fun formatDuration(seconds: Long): String {
     val secs = seconds % 60
     return "%02d:%02d".format(mins, secs)
 }
+
+@Composable
+private fun KeepScreenOn() {
+    val context = LocalContext.current
+    DisposableEffect(Unit) {
+        val window = (context as? android.app.Activity)?.window
+        window?.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
+        onDispose {
+            window?.clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
+        }
+    }
+}

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/call/CallManager.kt

@@ -56,6 +56,7 @@ class CallManager(
 
     private var timeoutJob: Job? = null
     private var resetJob: Job? = null
+    private val processedEventIds = mutableSetOf<String>()
 
     companion object {
         const val CALL_TIMEOUT_MS = 60_000L // 60 seconds ringing timeout
@@ -198,6 +199,7 @@ class CallManager(
 
     fun onSignalingEvent(event: Event) {
         if (isEventTooOld(event)) return
+        if (!processedEventIds.add(event.id)) return
 
         when (event) {
             is CallOfferEvent -> onIncomingCallEvent(event)
@@ -234,6 +236,7 @@ class CallManager(
         cancelTimeout()
         resetJob?.cancel()
         resetJob = null
+        processedEventIds.clear()
     }
 
     private fun transitionToEnded(