🔒 Fix command injection in Sandbox proxy teardown

[TrueAlpha-spiral]

🎯 What: Replaced execSync with execFileSync when stopping the sandbox proxy container.
⚠️ Risk: The previous implementation used string concatenation (execSync(config.command + ...)). If config.command was controlled by an external or untrusted source, it could allow arbitrary command injection on the host system.
🛡️ Solution: execFileSync(config.command, ['rm', '-f', SANDBOX_PROXY_NAME]) safely invokes the desired command using an array of arguments, completely bypassing the shell execution and preventing any command injection.

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PR created automatically by Jules for task 18420551017266452461 started by @TrueAlpha-spiral

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