feat(android): add voice protocol models and overlay mode enum

android/app/src/main/java/com/thisux/droidclaw/model/AppState.kt

@@ -28,3 +28,9 @@ data class GoalSession(
     val status: GoalStatus,
     val timestamp: Long = System.currentTimeMillis()
 )
+
+enum class OverlayMode {
+    Idle,
+    Listening,
+    Executing
+}

android/app/src/main/java/com/thisux/droidclaw/model/Protocol.kt

@@ -76,6 +76,23 @@ data class StopGoalMessage(
     val type: String = "stop_goal"
 )
 
+@Serializable
+data class VoiceStartMessage(
+    val type: String = "voice_start"
+)
+
+@Serializable
+data class VoiceChunkMessage(
+    val type: String = "voice_chunk",
+    val data: String
+)
+
+@Serializable
+data class VoiceStopMessage(
+    val type: String = "voice_stop",
+    val action: String
+)
+
 @Serializable
 data class ServerMessage(
     val type: String,