🛡️ Sentinel: [MEDIUM] Fix exception handling in admin login to prevent information leak

[shadowcoder8]

🚨 Severity: MEDIUM
💡 Vulnerability: The /admin/login/ route used a generic except Exception as e handler that caught all errors (including HTTPExceptions thrown by underlying logic, such as a 500 error for missing configuration) and blindly returned str(e) in the detail of a new 401 HTTPException. This incorrectly exposed raw internal string representations of exceptions directly to the client.
🎯 Impact: Potential leakage of sensitive internal details (e.g. database connection strings or missing configuration state) to unauthorized users.
🔧 Fix: Refactored the exception handling in main.py's /admin/login/ route. Explicitly caught and re-raised HTTPException to preserve intended responses (like 500 for missing config), and replaced the catch-all Exception block to log the detail internally while returning a sanitized generic error to the client. Also added a .jules/sentinel.md entry.
✅ Verification: Verified via an ad-hoc test script using mocks (since removed) that unconfigured credentials result in a proper 500 error and other exceptions are sanitized. All existing Pytest tests continue to pass.

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PR created automatically by Jules for task 17223080497846640034 started by @shadowcoder8

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