Potential fix for code scanning alert no. 3: Information exposure through an exception

[GitTimeraider]

Potential fix for https://github.com/GitTimeraider/GithubBackup-docker/security/code-scanning/3

To fix the problem, we should avoid exposing the raw exception message (str(e)) in API responses. Instead, the error should be logged at the server, and the user should be shown a generic message indicating an internal error. This change must be made in the /api/test-backup/<int:repo_id> endpoint, specifically in the exception handler in lines 542-543. Necessary changes include:

• Replace return jsonify({'success': False, 'error': str(e)}), 500 with a generic message like "An internal error occurred.".
• Add logging of the exception (with stack trace) for server-side diagnostics, if not already present.
• If necessary, ensure an appropriate logging facility (likely logger.error(..., exc_info=True)) is used.

No additional imports or dependencies are needed, as logging is already configured.

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[Copilot]

Pull Request Overview

This PR fixes a security vulnerability where raw exception messages were being exposed to users through the API response. The change prevents information leakage while maintaining proper error logging for debugging purposes.

• Replaces exposed exception details with a generic error message in the API response
• Adds server-side logging with full exception details for debugging

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