🛡️ Sentinel: [MEDIUM] Fix CWE-276 insecure file permissions

[rschumann]

🚨 Severity: MEDIUM
💡 Vulnerability: CWE-276: Insecure file permissions when writing registry and cache files (0644).
🎯 Impact: Unauthorized local users could read sensitive model discovery data and cached information.
🔧 Fix: Changed file creation permissions from 0644 to 0600 to restrict access solely to the owner.
✅ Verification: Verified via gosec ./... that the CWE-276 vulnerability is resolved.

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PR created automatically by Jules for task 1353051594169335279 started by @rschumann

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