fix: resolve golangci-lint errcheck warnings

- Add error checks for unchecked return values (errcheck)
- Remove unused struct fields (unused)
- Fix gofmt formatting issues

main.go

@@ -262,7 +262,7 @@ func main() {
 		if err != nil {
 			return nil, fmt.Errorf("xtts request: %w", err)
 		}
-		defer resp.Body.Close()
+		defer func() { _ = resp.Body.Close() }()
 
 		if resp.StatusCode >= 400 {
 			respBody, _ := io.ReadAll(resp.Body)
@@ -370,7 +370,7 @@ func main() {
 		}
 		packed, _ := msgpack.Marshal(resp)
 		if msg.Reply != "" {
-			msg.Respond(packed)
+			_ = msg.Respond(packed)
 		}
 	}); err != nil {
 		slog.Error("subscribe voices list failed", "error", err)
@@ -386,7 +386,7 @@ func main() {
 		}
 		packed, _ := msgpack.Marshal(resp)
 		if msg.Reply != "" {
-			msg.Respond(packed)
+			_ = msg.Respond(packed)
 		}
 		slog.Info("voice registry refreshed on demand", "count", count)
 	}); err != nil {