Bump version to v0.4.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: phiat

main.go

@@ -24,7 +24,7 @@ import (
 )
 
 var (
-	version = "0.3.1"
+	version = "0.4.0"
 )
 
 func main() {