unetd: 🛡️ Sentinel: [High] Fix command injection in network_keygen

[ManupaKDU]

🚨 Severity: High
💡 Vulnerability: Command injection in unet.uc via network_keygen because args and extra_args were directly interpolated into a sh -c string.
🎯 Impact: Arbitrary command execution if an attacker can control args or extra_args.
🔧 Fix: Use positional arguments with sh -c 'exec "$0" "$@" <&N' to safely pass arguments directly to unet-tool as an array without shell expansion.
✅ Verification: Ensured code is syntactically correct and verified build system integration via make help.

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PR created automatically by Jules for task 11916514846335463293 started by @manupawickramasinghe

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