platform: modularize api/gui, add docs-tests-web foundation, and refresh root config

selective-vpn-api/app/egressutil/probe.go

@@ -0,0 +1,19 @@
+package egressutil
+
+func ProbeFirstSuccess(endpoints []string, probe func(rawURL string) (string, error)) (string, []string) {
+	if len(endpoints) == 0 {
+		return "", nil
+	}
+	errs := make([]string, 0, len(endpoints))
+	for _, rawURL := range endpoints {
+		if probe == nil {
+			continue
+		}
+		val, err := probe(rawURL)
+		if err == nil {
+			return val, nil
+		}
+		errs = append(errs, err.Error())
+	}
+	return "", errs
+}