classify CloudFront distributions

Custom domains commonly CNAME to <dist>.cloudfront.net, so CDN-hosted static
sites were invisible to CNAME discovery. Classify them as AWS/WebApp and probe
https://<dist>.cloudfront.net/ for readability.

internal/classify/classify.go

@@ -114,6 +114,8 @@ func Classify(host string) (model.Match, bool) {
 	switch {
 	case strings.HasSuffix(host, ".amazonaws.com"):
 		return classifyAWS(&s)
+	case strings.HasSuffix(host, ".cloudfront.net"):
+		return classifyCloudFront(&s)
 	case strings.HasSuffix(host, ".core.windows.net"):
 		return classifyAzureCore(&s)
 	case strings.HasSuffix(host, ".database.windows.net"):