🛡️ Sentinel: [CRITICAL] Fix path traversal (Zip Slip) in skills import

[thirdeyenation]

🚨 Severity: CRITICAL
💡 Vulnerability: A path traversal (Zip Slip) vulnerability was found in helpers/skills_import.py where zipfile.ZipFile.extractall() was called on uploaded zip files without any path containment checks. A malicious zip file containing paths like ../../../etc/passwd could overwrite arbitrary files on the system during extraction.
🎯 Impact: Arbitrary File Overwrite / Remote Code Execution (RCE) if an attacker can upload a crafted skill zip file.
🔧 Fix: Updated _unzip_to_temp_dir to explicitly resolve the target directory and iterate through every file in the zip archive (z.namelist()), verifying that each file's resolved path is completely contained within the target extraction directory (Path.is_relative_to()) before performing the extraction. If any file attempts to escape the directory, extraction is safely aborted with a ValueError.
✅ Verification: Ran unit tests specifically testing safe extraction and catching unsafe extraction paths successfully, confirming the protection is active.

---

PR created automatically by Jules for task 14245286688391670179 started by @thirdeyenation

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.