🛡️ Sentinel: [CRITICAL] Fix Path Traversal in ApiFilesGet

[thirdeyenation]

• 🚨 Severity: CRITICAL
• 💡 Vulnerability: The ApiFilesGet handler allowed arbitrary file reads due to missing path traversal checks on user-provided file paths.
• 🎯 Impact: An attacker with API access could read sensitive system or application files (e.g., configuration, /etc/passwd).
• 🔧 Fix: Implemented files.is_in_base_dir() check to ensure requested files are within the application's allowed directory boundary.
• ✅ Verification: Tested with traversal payloads ensuring they are blocked by the security validation.

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PR created automatically by Jules for task 3564970281160076888 started by @thirdeyenation

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