Add character portrait display feature.

shared/src/commonMain/kotlin/com/pixelized/shared/lwa/protocol/websocket/GameEvent.kt

@@ -0,0 +1,13 @@
+package com.pixelized.shared.lwa.protocol.websocket
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+sealed interface GameEvent : SocketMessage {
+
+    @Serializable
+    data class DisplayPortrait(
+        override val timestamp: Long,
+        val characterSheetId: String?,
+    ) : GameEvent
+}