🛡️ Sentinel: [security improvement] Secure Process Execution for docker system prune

[acebytes]

This PR replaces a shell wrapper execution (/bin/bash -c "docker system prune -f 2>&1") with direct binary execution (/usr/bin/env docker ...) using Process in dockerPrune.

This is a defense-in-depth enhancement. While no dynamic user input was passed to the shell wrapper, relying on a shell to execute fixed commands is an anti-pattern. By executing the binary directly and replicating the shell redirection (2>&1) securely within Swift using Pipe(), we eliminate the shell environment and its associated attack surface entirely.

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PR created automatically by Jules for task 9862449520480688010 started by @acebytes

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