⚡ Bolt: Unblock MainActor during Docker prune and disk scans

[acebytes]

💡 What: Offload synchronous I/O operations from the @MainActor in CacheoutViewModel.
🎯 Why: Foundation.Process.waitUntilExit(), readDataToEndOfFile(), and DiskInfo.current() all execute synchronously on the thread they are called from. Because CacheoutViewModel runs on the @MainActor, executing these operations directly causes the main thread to block, freezing the UI completely during the execution of a Docker prune or the initial disk space check. By wrapping them in Task.detached, we execute them on background threads while the UI remains responsive.
📊 Impact: Completely eliminates UI freezes and unresponsiveness during scan() operations (which fetch disk stats) and Docker pruning (which shells out to docker system prune -f). The app remains completely fluid.
🔬 Measurement: Observe the UI during a scan or Docker prune (when isScanning or isDockerPruning state properties change the UI) to verify that spinning progress indicators no longer freeze and the app window remains draggable.

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PR created automatically by Jules for task 10533459610125003356 started by @acebytes

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