Increase speedtest default size to 50MB

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

Author: vintikzzz

services/speedtest.go

@@ -12,7 +12,7 @@ import (
 )
 
 const (
-	speedtestDefaultSize = 10 * 1024 * 1024 // 10MB
+	speedtestDefaultSize = 50 * 1024 * 1024 // 50MB
 )
 
 type SpeedTest struct {