Detect/mitigate stuck Docker builds

We received a report of a Docker build getting stuck, reporting no status, and never completing. It first happened after a Live Update crash fallback, but the same behavior happened after a fresh tilt up. The user was able to get things to proceed after running a docker system prune.

Given these conditions, it seems less likely to be a pure Tilt bug, but the experience is frustrating, particularly because there's no practical way to address it within Tilt.

I think there might be several possible improvements here:

• Have a (configurable?) timeout for max duration w/o any activity from BuildKit
• Possibility to trigger a from-scratch build, e.g. docker build --no-cache ... to eliminate bad intermediary containers
• Detect critically low / out of disk space [probably tricky w/ Docker for Mac/Windows and their hidden VMs] and suggest running prune (or triggering an immediate/more aggressive tilt docker prune)

No files, tests, or entry points are named. Start by reproducing the stuck build with tilt up, compare behavior before and after docker system prune, and investigate the BuildKit activity and disk-space conditions described here. Done would require selecting and validating a concrete mitigation, such as timeout handling, a from-scratch build option, or actionable disk-space guidance.