🛡️ Sentinel: [HIGH] Fix command injection risk in unix id-lookups

[Donach]

🚨 Severity: HIGH
💡 Vulnerability: The id-lookups.ts functions (getGidFromGroupName, getUidFromUsername, getHomedirFromUsername) previously used execSync with string interpolation. This means variables were evaluated in a shell, allowing possible command injection via shell metacharacters.
🎯 Impact: A maliciously crafted username or groupname could be exploited to run arbitrary commands in the daemon context, leading to remote code execution.
🔧 Fix: Replaced execSync with execFileSync. Passed the dynamic variables strictly as arguments via an array and enforced the -- separator to prevent argument injection if an input starts with -.
✅ Verification: Ran pnpm lint and pnpm test successfully. Confirmed execFileSync implementation is intact and robust.

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PR created automatically by Jules for task 14796835733922872536 started by @Donach

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