Show live progress while the TUI scans and deletes

[UnbreakableMJ]

Summary

The TUI froze during its two long operations — the delete loop and the scan both ran synchronously on the UI thread, so event_loop never redrew. With large roots now reachable (/spacecraft-software, /), scanning could freeze the screen for seconds with no feedback.

This moves both operations onto a background worker thread (std::thread + mpsc — no new dependencies) feeding a live progress overlay:

• Deleting — spinner + [done/total] + "freed X of Y" + a determinate Gauge. esc cancels after the current item (cooperative AtomicBool), then it auto-rescans.
• Scanning (startup, post-delete, post-picker) — spinner naming the current category. esc quits (the read-only scan thread is safely abandoned). Scan errors are now non-fatal — shown in the overlay instead of crashing the TUI.
• The event loop pumps the channel each tick and animates at ~12 fps (ACTIVE_TICK 80 ms) only while a job runs; idle stays at 250 ms, so no extra CPU at rest.
• Safety unchanged: deletions stay bounded by the same roots and safety::check_deletable. The worker only moves Send data (Candidate/Deleter/Outcome).

Docs

• Texinfo "Interactive TUI" gains a Progress section (builds zero-warning).
• AGENTS.md and SKILL.md note the overlay.

Testing

• cargo fmt --check · cargo clippy --workspace --all-targets -- -D warnings · cargo test --workspace (45 pass — new progress_ratio unit test) · reuse lint compliant · makeinfo zero-warning.
• Reinstalled to ~/.cargo/bin/vacuum.
• Caveat: the live overlay/threading needs a TTY and is not unit-tested — coverage lives in the pure progress_ratio helper. Worth a manual smoke-test: vacuum tui /spacecraft-software (scan spinner cycles categories); select large items → enter → y (gauge fills); esc mid-delete cancels cleanly.

Out of scope / follow-ups

• Interrupting a single in-flight remove_dir_all/jwalk (cancel is between items / between cleaners only).
• Parallelizing deletion across items (kept sequential for predictable safety ordering and simple progress accounting).

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