fix: move ipcMsgTypeOpus constant to source.go for cross-platform builds

internal/audio/cgo_source.go

@@ -22,7 +22,6 @@ import (
 
 const (
 	ipcMaxFrameSize = 1024 // Max Opus frame size: 128kbps @ 20ms = ~600 bytes
-	ipcMsgTypeOpus  = 0    // Message type for Opus audio data
 )
 
 // CgoSource implements AudioSource via direct CGO calls to C audio functions (in-process)

internal/audio/source.go

@@ -1,5 +1,10 @@
 package audio
 
+// IPC message types
+const (
+	ipcMsgTypeOpus = 0 // Message type for Opus audio data
+)
+
 // AudioSource provides audio frames via CGO (in-process) C audio functions
 type AudioSource interface {
 	// ReadMessage reads the next audio message