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

[acebytes]

Security Context

🛡️ Sentinel: [security improvement]

• 💡 What: Refactored dockerPrune() in CacheoutViewModel.swift to execute the docker binary directly instead of relying on a shell wrapper (/bin/bash -c).
• 🎯 Why: Mitigates the risk of command injection vulnerabilities by passing command arguments explicitly rather than constructing a shell string.
• 🔧 Fix: Replaced /bin/bash with /usr/bin/env and explicitly passed ["docker", "system", "prune", "-f"] to process.arguments. Redirection (2>&1) was securely replicated by pointing both process.standardOutput and process.standardError to the same Pipe() instance.
• ✅ Verification: Code review verifies equivalent behavior while safely dropping the shell dependency. Local tests are unsupported on the Linux-based environment. A sentinel journal entry has been created to document this pattern.

---

PR created automatically by Jules for task 1176384545504016667 started by @acebytes

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.