🛡️ Sentinel: [HIGH] Fix Path Traversal (Zip Slip) in Skill Imports

[thirdeyenation]

🚨 Severity: HIGH
💡 Vulnerability: Path Traversal (Zip Slip) vulnerability in helpers/skills_import.py where uploaded ZIP files were extracted using zipfile.extractall() without verifying if the individual file paths safely remain within the intended destination directory.
🎯 Impact: A maliciously crafted archive could bypass path containment, allowing an attacker to write files anywhere on the filesystem that the application process has permissions to access (e.g. overwriting configurations or dropping executable code).
🔧 Fix: Iterated through z.namelist() and resolved each member's extraction path. Added a strict check using Path.is_relative_to() to ensure every resolved path remains inside the target extraction folder. If any unsafe path is detected, it raises a ValueError to block the extraction entirely.
✅ Verification: Run the standard test suite to ensure standard skills still import correctly, and check the code to see that z.namelist() is inspected before extraction.

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PR created automatically by Jules for task 5553890262309735703 started by @thirdeyenation

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