Add backend foundation and config-driven workbench

backend/internal/apperr/apperr.go

@@ -0,0 +1,29 @@
+package apperr
+
+import "errors"
+
+type Error struct {
+	Status  int    `json:"-"`
+	Code    string `json:"code"`
+	Message string `json:"message"`
+}
+
+func (e *Error) Error() string {
+	return e.Message
+}
+
+func New(status int, code, message string) *Error {
+	return &Error{
+		Status:  status,
+		Code:    code,
+		Message: message,
+	}
+}
+
+func From(err error) *Error {
+	var appErr *Error
+	if errors.As(err, &appErr) {
+		return appErr
+	}
+	return nil
+}