🛡️ Sentinel: [CRITICAL] Fix cross-platform path traversal vulnerabilities

[rschumann]

🚨 Severity: CRITICAL
💡 Vulnerability: Path traversal vulnerabilities where input validation solely relies on os.PathSeparator instead of checking for both / and \ across platforms.
🎯 Impact: Malicious actors could supply path strings using \ on non-Windows platforms or / on Windows systems to bypass single-separator checks and execute path traversal attacks (e.g., uploading/deleting arbitrary files, reading out-of-bounds data).
🔧 Fix: Replaced strings.Contains(name, string(os.PathSeparator)) and strings.ContainsRune(id, os.PathSeparator) with strings.ContainsAny(..., "/\\") to robustly catch cross-platform path traversal attempts in management handlers and storage backends.
✅ Verification: Automated tests pass and manual code review confirms standard cross-platform validation pattern.

---

PR created automatically by Jules for task 4637435235847606748 started by @rschumann

[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.