feat(clean): add opt-in Docker unused data pruning

[MohammedTarigg]

Summary

This PR adds opt-in Docker cleanup to mo clean.

1. Adds a --docker flag for explicit Docker pruning.
2. Keeps default mo clean behavior safe by skipping Docker unused data unless the flag is set.
3. Updates help/docs and adds tests for opt-in, daemon-down, and active prune paths.

Related: local storage audit follow-up

Scope

• In scope: opt-in pruning of unused Docker images, stopped containers, unused networks, and anonymous volumes during mo clean.
• Out of scope: automatic Docker pruning in default clean runs, interactive prompts, or broader Docker UX changes.
• Platform scope: macOS with Docker CLI/Desktop available.

Why This Approach

• Docker data can be large, but pruning images and volumes can remove local dev state users still expect to keep.
• An explicit --docker flag keeps the default cleanup flow conservative while still making the reclaim path easy to discover and script.
• This uses docker system prune -af --volumes because it matches the reclaimable buckets users see in docker system df better than docker builder prune alone.

Validation

• bash -n bin/clean.sh lib/core/help.sh lib/clean/dev.sh mole tests/clean_dev_caches.bats
• bats tests/clean_dev_caches.bats
• Local manual validation:
  • docker system df
  • docker system prune -a --volumes -f

Notes

• Default mo clean now prints a clear skip message for Docker unused data and points users to --docker.
• On my local machine, Docker Desktop data dropped from about 15G to 1.2G after prune, and free disk increased from 53Gi to 67Gi.