Previously, fan-out skipped any existing real directory not recorded in
the lock file, treating it as user content. This left stale skill copies
installed by other tools (e.g. npx skills add) permanently out of date.
Now: if the directory contains a SKILL.md, it is recognized as a skill
artifact and replaced with a symlink to the canonical dir. Directories
without SKILL.md are still preserved (user content safety boundary).
故璃