🛡️ Sentinel: [CRITICAL] Fix path traversal in skill imports

[thirdeyenation]

🚨 Severity: CRITICAL
💡 Vulnerability: Zip Slip (path traversal) vulnerability in helpers/skills_import.py when using extractall() to extract imported skills.
🎯 Impact: A malicious skill zip could contain file paths like ../../ allowing an attacker to overwrite arbitrary files on the system outside the designated import directory.
🔧 Fix: Validated all entries in z.namelist() using is_relative_to() before allowing extractall() to proceed.
✅ Verification: Review the code to ensure is_relative_to is used on resolved paths. Run test suite.

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PR created automatically by Jules for task 16398020178096808090 started by @thirdeyenation

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