🛡️ Sentinel: Fix information leakage in login_required error response

[Pmaster-dev]

🛡️ Sentinel Security Fix: Prevent Information Leakage in Authentication

🚨 Severity: MEDIUM
💡 Vulnerability: Raw exception messages (str(e)) were returned in JSON responses by the login_required decorator when JWT verification failed or errors occurred.
🎯 Impact: Untrusted clients could receive internal system details, database connection strings, or stack trace fragments.
🔧 Fix: Omitted raw exception string from response payload and logged it server-side using logger.exception().
✅ Verification: Added unit test tests/test_auth_utils.py verifying that exception details are not present in error responses and ran unittest suite.

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PR created automatically by Jules for task 2465454228130646528 started by @Pmaster-dev

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