🛡️ Sentinel: Fix sensitive error detail leakage in login_required

[Pmaster-dev]

🛡️ Sentinel: Fix sensitive error detail leakage in login_required

🚨 Severity: MEDIUM
💡 Vulnerability: The login_required decorator in auth/utils.py returned raw exception details (str(e)) in 401 response payloads.
🎯 Impact: An attacker could deliberately trigger auth exceptions to inspect internal stack traces or database/token errors.
🔧 Fix: Removed str(e) leakage and return generic {"error": "Unauthorized"} response.
✅ Verification: Added unit tests in tests/test_auth.py verifying response behavior when JWT verification fails with exceptions.

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PR created automatically by Jules for task 4846975491480150802 started by @Pmaster-dev

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