🛡️ Sentinel: [security improvement] Refactor dockerPrune to direct binary execution

[acebytes]

🛡️ Sentinel: Security improvement

💡 What: Refactored the docker system prune command execution in CacheoutViewModel from relying on an arbitrary /bin/bash -c shell invocation to secure, direct binary execution via /usr/bin/env docker.
🎯 Why: Direct binary execution is a standard defense-in-depth security practice that completely sidesteps shell features like globs, pipelines, and variables. It hardens the process execution against shell injection vulnerabilities should argument generation ever become dynamic.
🔧 Fix: Changed process.executableURL from /bin/bash to /usr/bin/env, passed explicit arguments ["docker", "system", "prune", "-f"], and inherently handled 2>&1 via assigning Pipe() to both stdout and stderr.
✅ Verification: Ran pre-commit checks and code review verified the refactor safely maintains all functionality while removing shell overhead.

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PR created automatically by Jules for task 15183117915956383475 started by @acebytes

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