fix: clean up rejected peer's PeerSession to prevent stale sessions blocking hangup

When a peer rejects a group call, CallManager updated its state but never
notified CallController to dispose the peer's PeerSession. This caused two
issues:

1. The rejected peer's PeerConnection lingered in HAVE_LOCAL_OFFER state
   until the entire call ended (resource leak visible as "disposing 2 peer
   sessions" when only 1 should exist).

2. In onPeerDisconnected, the allDisconnected check required ALL sessions
   to be CLOSED. The stale session blocked this check, preventing automatic
   hangup when ICE failed — meaning the remote peer never received a hangup
   event and kept ringing.

Fix: invoke onPeerLeft when a peer rejects in Offering/Connecting/Connected
states, and make onPeerDisconnected treat sessions without a remote
description as inactive.

https://claude.ai/code/session_01UXaFKmHVPDyTzfHL8fkSw1

amethyst/src/main/java/com/vitorpamplona/amethyst/service/call/CallController.kt

@@ -729,12 +729,17 @@ class CallController(
 
     private fun onPeerDisconnected(peerPubKey: HexKey) {
         Log.d(TAG) { "Peer ${peerPubKey.take(8)} disconnected (ICE FAILED)" }
-        // If all peers disconnected, hang up
+        // If all peers disconnected, hang up.
-        val sessionStates = peerSessions.map { (key, ps) -> "${key.take(8)}=${ps.session.getSignalingState()}" }
+        // A session counts as "not active" if it is the one that just failed,
+        // if it was already closed, or if it never received a remote description
+        // (e.g. the peer rejected before answering).
+        val sessionStates = peerSessions.map { (key, ps) -> "${key.take(8)}=${ps.session.getSignalingState()},remoteSet=${ps.remoteDescriptionSet.get()}" }
         Log.d(TAG) { "onPeerDisconnected: checking remaining sessions: $sessionStates" }
         val allDisconnected =
             peerSessions.keys.all { key ->
-                key == peerPubKey || peerSessions[key]?.session?.getSignalingState() == PeerConnection.SignalingState.CLOSED
+                key == peerPubKey ||
+                    peerSessions[key]?.session?.getSignalingState() == PeerConnection.SignalingState.CLOSED ||
+                    peerSessions[key]?.remoteDescriptionSet?.get() != true
             }
         if (allDisconnected) {
             Log.d(TAG) { "onPeerDisconnected: all peers disconnected, hanging up" }

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

@@ -349,6 +349,7 @@ class CallManager(
                     transitionToEnded(current.callId, current.peerPubKeys, EndReason.PEER_REJECTED)
                 } else {
                     _state.value = current.copy(peerPubKeys = remaining)
+                    onPeerLeft?.invoke(rejectingPeer)
                 }
             }
 
@@ -356,12 +357,14 @@ class CallManager(
                 if (callId != current.callId) return
                 _state.value =
                     current.copy(pendingPeerPubKeys = current.pendingPeerPubKeys - rejectingPeer)
+                onPeerLeft?.invoke(rejectingPeer)
             }
 
             is CallState.Connected -> {
                 if (callId != current.callId) return
                 _state.value =
                     current.copy(pendingPeerPubKeys = current.pendingPeerPubKeys - rejectingPeer)
+                onPeerLeft?.invoke(rejectingPeer)
             }
 
             is CallState.IncomingCall -> {