move CaptchaError to a separate file to avoid circular import errors

packages/backend/src/misc/captcha-error.ts

@@ -0,0 +1,18 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { CaptchaErrorCode } from '@/core/CaptchaService.js';
+
+export class CaptchaError extends Error {
+	public readonly code: CaptchaErrorCode;
+	public readonly cause?: unknown;
+
+	constructor(code: CaptchaErrorCode, message: string, cause?: unknown) {
+		super(message, cause ? { cause } : undefined);
+		this.code = code;
+		this.cause = cause;
+		this.name = 'CaptchaError';
+	}
+}