macOS full disk: check hidden AssetsV2 and update snapshots

When a Mac reports ~40GB more used than du can find, look at /System/Volumes/Data/System/Library/AssetsV2 (iOS/xrOS simulator runtimes and staged macOS updates live there — 25GB+ is common) and APFS com.apple.os.update snapshots from a staged-but-unfinished update; installing the pending update releases them. Also: du -sh ~/* misses dotfolders — ~/.npm _cacache and ~/.cache/uv were 12GB each, both safely cleared via npm cache clean --force and uv cache clean. mdls kMDItemLastUsedDate can fail; preference file mtimes in ~/Library/Preferences are a reliable fallback for app last-use.