refactor(auth): merge cap domain plugin into auth

backend/plugins/domain/auth/pow/errs.go

@@ -0,0 +1,15 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package pow
+
+const (
+	errInvalidTokenFormat = "invalid token format"
+	errInvalidHeader      = "invalid header"
+	errSignatureMismatch  = "signature mismatch"
+	errInvalidToken       = "invalid_token"
+	errScopeMismatch      = "scope_mismatch"
+	errExpired            = "expired"
+	errInvalidSolutions   = "invalid_solutions"
+	errInvalidSolution    = "invalid_solution"
+)