🛡️ Sentinel: [CRITICAL] Fix command injection in unix system queries

[Donach]

🚨 Severity: CRITICAL
💡 Vulnerability: The daemon used execSync from node:child_process in packages/core/src/unix/system-queries.ts to execute shell commands like getent and id which took dynamic parameters like username or groupName. Due to the usage of double quotes around parameters being interpreted by a shell environment, this resulted in a command injection vulnerability.
🎯 Impact: If an attacker can control the username or groupName inputs, they could break out of the double quotes and execute arbitrary shell commands on the host operating system with the privileges of the daemon.
🔧 Fix: Replaced execSync with execFileSync, completely removing the implicit shell execution. It now securely passes arguments directly to the executable binaries (id and getent), eliminating the command injection vector. Unused imports in system-queries.ts were also cleaned up.
✅ Verification: Verified by running the relevant core unix tests (pnpm --filter @agor/core test -- src/unix/system-queries.ts src/unix/group-manager.test.ts src/unix/user-manager.test.ts src/unix/run-as-user.test.ts) and workspace linter (pnpm -w run lint:fix). All checks passed cleanly.

Note: The journal file .jules/sentinel.md was also updated with these learnings.

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PR created automatically by Jules for task 6320002034556739945 started by @Donach

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