repo-hygiene: dry-run emits no sizes and apply re-enumerates — no manifest, no resume, gate pays the walk twice

[kyle-sexton]

Problem

Three coupled gaps in the dry-run→confirm→apply flow:

1. No sizes. Planned remove: lines carry no per-path or total size, so the confirmation gate cannot state reclaimable space; the session needed a second manual du pass to tell the user "~3.3 GB".
2. Apply re-enumerates. --apply re-runs the same full walks the dry-run just did (cost doubled; see the find-perf issue for walk cost).
3. No manifest/resume. A killed apply leaves partial state with no record of what remains; discovering it costs another full walk. (Removal is idempotent, so correctness holds — only cost.)

Fix direction

Dry-run writes a manifest (path + size + class); the confirm gate surfaces the totals; --apply consumes the manifest (with a staleness guard, e.g. re-stat before rm) instead of re-walking; resume = re-apply surviving manifest entries.