refactor(auth): merge cap domain plugin into auth

backend/plugins/domain/auth/cap_errs.go

@@ -0,0 +1,23 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package auth
+
+// HTTP 响应错误文案
+const (
+	errCapTokenMissing          = "验证码验证失败，缺少验证码凭证" //nolint:gosec // false positive: this is an error message, not hardcoded credentials
+	errCapTokenInvalidOrExpired = "验证码校验失败或已过期，请重试" //nolint:gosec // false positive: this is an error message, not hardcoded credentials
+	errCapNotConfigured         = "captcha is not configured"
+	errChallengeGenerateFailed  = "生成验证难题失败，请稍后再试"
+	errInvalidRequestParams     = "无效的参数"
+	errSolutionVerifyFailed     = "校验验证解答失败，请稍后再试"
+)
+
+// Redeem 结果码，属于 redeem 响应 JSON 的对外契约取值，禁止改写取值
+const (
+	redeemErrInvalidToken     = "invalid_token"
+	redeemErrNonceStoreFailed = "nonce_store_error"
+	redeemErrAlreadyRedeemed  = "already_redeemed"
+	redeemErrSettingsLoad     = "settings_load_error"
+	redeemErrTokenStoreFailed = "token_store_error" //nolint:gosec // error code, not hardcoded credentials
+)