refactor: improve separation of concerns in call feature

1. Move UI toggle state out of CallState.Connected:
   - Removed isAudioMuted/isVideoEnabled/isSpeakerOn from domain
     CallState. These are UI concerns, not call state.
   - Added StateFlows for toggles in CallController (isAudioMuted,
     isVideoEnabled, isSpeakerOn) with proper toggle methods.
   - CallScreen reads toggle state from CallController flows.
   - Removed toggleAudioMute/toggleVideo/toggleSpeaker from
     CallManager (no longer manages UI state).

2. Move ICE candidate parsing to quartz layer:
   - Added candidateSdp(), sdpMid(), sdpMLineIndex() parsers and
     serializeCandidate() to CallIceCandidateEvent in quartz.
   - Removed companion object with parseIceCandidate/
     serializeIceCandidate from CallController.
   - CallController now uses quartz-layer parsing directly.
   - Updated IceCandidateSerializationTest accordingly.

3. Add helper methods to CallManager:
   - currentCallId() and currentPeerPubKey() extract from any
     active state, reducing repeated when expressions.

4. Fix empty callId bug in ChatroomScreen:
   - Navigation to ActiveCall now uses callManager.currentCallId()
     instead of hardcoded empty string.

https://claude.ai/code/session_017hZm7yu7CzmcQgZGSaqSXS

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nipACWebRtcCalls/events/CallIceCandidateEvent.kt

@@ -45,11 +45,32 @@ class CallIceCandidateEvent(
 
     fun candidateJson() = content
 
+    fun candidateSdp(): String = CANDIDATE_REGEX.find(content)?.groupValues?.get(1) ?: ""
+
+    fun sdpMid(): String = SDP_MID_REGEX.find(content)?.groupValues?.get(1) ?: "0"
+
+    fun sdpMLineIndex(): Int =
+        SDP_MLINE_INDEX_REGEX
+            .find(content)
+            ?.groupValues
+            ?.get(1)
+            ?.toIntOrNull() ?: 0
+
     companion object {
         const val KIND = 25052
         const val ALT_DESCRIPTION = "WebRTC ICE candidate"
         const val EXPIRATION_SECONDS = 20L
 
+        private val CANDIDATE_REGEX = """"candidate"\s*:\s*"([^"]*)"""".toRegex()
+        private val SDP_MID_REGEX = """"sdpMid"\s*:\s*"([^"]*)"""".toRegex()
+        private val SDP_MLINE_INDEX_REGEX = """"sdpMLineIndex"\s*:\s*(\d+)""".toRegex()
+
+        fun serializeCandidate(
+            sdp: String,
+            sdpMid: String,
+            sdpMLineIndex: Int,
+        ): String = """{"candidate":"$sdp","sdpMid":"$sdpMid","sdpMLineIndex":$sdpMLineIndex}"""
+
         fun build(
             candidateJson: String,
             peerPubKey: HexKey,