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

selective-vpn-api/app/transport_singbox_profiles_errors.go

@@ -0,0 +1,26 @@
+package app
+
+import "strings"
+
+func errSingBoxProfileMode() error {
+	return &singBoxProfileError{text: "mode must be typed|raw"}
+}
+
+func errSingBoxProfileID() error {
+	return &singBoxProfileError{text: "invalid profile id"}
+}
+
+func errSingBoxProfileExists() error {
+	return &singBoxProfileError{text: "profile already exists"}
+}
+
+type singBoxProfileError struct {
+	text string
+}
+
+func (e *singBoxProfileError) Error() string {
+	if e == nil {
+		return "singbox profile error"
+	}
+	return strings.TrimSpace(e.text)
+}