feat: auto-load .env via shared internal/env package

Add godotenv dependency and internal/env init loader so all cmd/
scripts get .env vars loaded automatically via blank import.

go-util/cmd/gitea-leave-orgs/main.go

@@ -8,6 +8,8 @@ import (
 	"net/http"
 	"os"
 	"strings"
+
+	_ "github.com/tiennm99/go-util/internal/env"
 )
 
 // org represents a Gitea organization.